diff --git a/server/AyaNova/biz/PartBiz.cs b/server/AyaNova/biz/PartBiz.cs
index db79907c..9ef8db17 100644
--- a/server/AyaNova/biz/PartBiz.cs
+++ b/server/AyaNova/biz/PartBiz.cs
@@ -237,6 +237,52 @@ namespace AyaNova.Biz
         }
 
 
+        ////////////////////////////////////////////////////////////////////////////////////////////////
+        //APPEND SERIALS - called by PO ops to add serials to a part
+        //
+        internal static async Task AppendSerialsAsync(long partId, string serialText, AyContext ct, long UserId)
+        {
+            if (string.IsNullOrWhiteSpace(serialText)) return;
+            var serials = System.Text.RegularExpressions.Regex.Split(serialText, "[\\s,]+", System.Text.RegularExpressions.RegexOptions.IgnoreCase,
+                                       TimeSpan.FromMilliseconds(2000)).Select(x => x.Trim()).Where(x => !string.IsNullOrWhiteSpace(x)).Distinct().OrderBy(x => x).ToArray();
+            int nAdded = 0;
+            var ExistingSerials = await ct.PartSerial.Where(z => z.PartId == partId).OrderBy(z => z.Serial).ToListAsync();
+            //Add any new ones
+            foreach (string s in serials)
+            {
+                if (!ExistingSerials.Any(z => z.Serial == s))
+                {
+                    ct.PartSerial.Add(new PartSerial() { Serial = s, PartId = partId });
+                    nAdded++;
+                }
+            }
+            await ct.SaveChangesAsync();
+            await EventLogProcessor.LogEventToDatabaseAsync(new Event(UserId, partId, AyaType.Part, AyaEvent.Modified, $"LT:PartSerialNumbersAvailable change (+{nAdded})"), ct);
+        }
+
+        ////////////////////////////////////////////////////////////////////////////////////////////////
+        //REMOVE SERIALS - called by PO ops to remove serials from a part
+        //
+        internal static async Task RemoveSerialsAsync(long partId, string serialText, AyContext ct, long UserId)
+        {
+            if (string.IsNullOrWhiteSpace(serialText)) return;
+            var serials = System.Text.RegularExpressions.Regex.Split(serialText, "[\\s,]+", System.Text.RegularExpressions.RegexOptions.IgnoreCase,
+                                    TimeSpan.FromMilliseconds(2000)).Select(x => x.Trim()).Where(x => !string.IsNullOrWhiteSpace(x)).Distinct().OrderBy(x => x).ToArray();
+
+            int nRemoved = 0;
+            var ExistingSerials = await ct.PartSerial.Where(z => z.PartId == partId).OrderBy(z => z.Serial).ToListAsync();
+            foreach (PartSerial ps in ExistingSerials)
+            {
+                if (serials.Contains(ps.Serial))
+                {
+                    ct.PartSerial.Remove(ps);
+                    nRemoved++;
+                }
+            }
+            await ct.SaveChangesAsync();
+            await EventLogProcessor.LogEventToDatabaseAsync(new Event(UserId, partId, AyaType.Part, AyaEvent.Modified, $"LT:PartSerialNumbersAvailable change (-{nRemoved})"), ct);
+        }
+
 
         ////////////////////////////////////////////////////////////////////////////////////////////////
         //UPDATE STOCK LEVELS
@@ -412,7 +458,7 @@ namespace AyaNova.Biz
                 AddError(ApiErrorCode.VALIDATION_REFERENTIAL_INTEGRITY, "generalerror", await Translate("PartInventoryList"));//translates to "Part inventory"
             if (await ct.PartStockLevel.AnyAsync(m => m.PartId == inObj.Id))
                 AddError(ApiErrorCode.VALIDATION_REFERENTIAL_INTEGRITY, "generalerror", await Translate("PartStockingLevels"));
-             if (await ct.PurchaseOrderItem.AnyAsync(m => m.PartId == inObj.Id))
+            if (await ct.PurchaseOrderItem.AnyAsync(m => m.PartId == inObj.Id))
                 AddError(ApiErrorCode.VALIDATION_REFERENTIAL_INTEGRITY, "generalerror", await Translate("PurchaseOrder"));
 
         }
diff --git a/server/AyaNova/biz/PurchaseOrderBiz.cs b/server/AyaNova/biz/PurchaseOrderBiz.cs
index 8bd7c66b..8e136956 100644
--- a/server/AyaNova/biz/PurchaseOrderBiz.cs
+++ b/server/AyaNova/biz/PurchaseOrderBiz.cs
@@ -449,6 +449,8 @@ namespace AyaNova.Biz
                         return;
                     }
 
+                    await PartBiz.AppendSerialsAsync(poItem.PartId, poItem.Serials, ct, UserId);
+
                     //MIGRATE_OUTSTANDING - update workorderitempart here if applicable
                 }
 
@@ -461,6 +463,7 @@ namespace AyaNova.Biz
             //MODIFIED 
             if (ayaEvent == AyaEvent.Modified)
             {
+
                 //any old po items deleted?
                 foreach (var oldItem in oldObj.Items)
                 {
@@ -486,15 +489,24 @@ namespace AyaNova.Biz
                                 AddError(ApiErrorCode.API_SERVER_ERROR, "generalerror", $"Error updating inventory ({i.Description}):{pib.GetErrorsAsString()}");
                                 return;
                             }
+                            //might have serials so remove those as well
+                            await PartBiz.RemoveSerialsAsync(oldItem.PartId, oldItem.Serials, ct, UserId);
                         }
                     }
                 }
 
+                //ITERATE NEW ITEMS LOOK FOR CHANGES
                 foreach (var newItem in newObj.Items)
                 {
-                    //get the matching currentPoItem
+                    //get the matching oldItem
                     var oldItem = oldObj.Items.FirstOrDefault(z => z.Id == newItem.Id);
 
+                    //CHANGED THE VENDOR? (this doesn't preclude other changes as well below)
+                    if (oldObj.VendorId != newObj.VendorId)
+                    {
+                        SetPoItemDefaultPartValues(newItem, PoParts, newObj.VendorId);
+                    }
+
                     //NEW ITEM ADDED
                     if (oldItem == null)
                     {
@@ -514,28 +526,13 @@ namespace AyaNova.Biz
                                 return;
                             }
 
-                            if (!string.IsNullOrWhiteSpace(newItem.Serials))
-                            {
-                                //javascript version at UI for partserials entry
-                                //let splitted = this.newSerial.split(/[\s,]+/).filter(Boolean); //filter Boolean is equivalent to array.filter(item => Boolean(item)) and it's to filter out nulls concisely from badly formatted strings
-                                // splitted = [...splitted, ...this.obj];
-                                //   let uniqueItems = [...new Set(splitted)];
-                                //   uniqueItems.sort();
-
-                                //c# version to replicate above
-                                var serials = System.Text.RegularExpressions.Regex.Split(newItem.Serials, "[\\s,]+", System.Text.RegularExpressions.RegexOptions.IgnoreCase,
-                                     TimeSpan.FromMilliseconds(2000)).Select(x => x.Trim()).Where(x => !string.IsNullOrWhiteSpace(x)).Distinct().OrderBy(x => x).ToArray();
-
-
-
-
-                            }
+                            await PartBiz.AppendSerialsAsync(newItem.PartId, newItem.Serials, ct, UserId);
                         }
 
                         SetPoItemDefaultPartValues(newItem, PoParts, newObj.VendorId);
 
                         //MIGRATE_OUTSTANDING - update workorderitempart here if applicable
-                        continue;//on to next item
+                        continue;//on to next item no possible other changes here
                     }
 
                     //CHANGED PART OR WAREHOUSE ID
@@ -557,6 +554,8 @@ namespace AyaNova.Biz
                                 AddError(ApiErrorCode.API_SERVER_ERROR, "generalerror", $"Error updating inventory ({i.Description}):{pib.GetErrorsAsString()}");
                                 return;
                             }
+
+                            await PartBiz.RemoveSerialsAsync(oldItem.PartId, oldItem.Serials, ct, UserId);
                         }
 
                         if (newItem.QuantityReceived > 0)
@@ -574,13 +573,15 @@ namespace AyaNova.Biz
                                 AddError(ApiErrorCode.API_SERVER_ERROR, "generalerror", $"Error updating inventory ({i.Description}):{pib.GetErrorsAsString()}");
                                 return;
                             }
+
+                            await PartBiz.AppendSerialsAsync(newItem.PartId, newItem.Serials, ct, UserId);
                         }
 
                         //Update part values into poitem if the part or vendor has changed 
                         if (oldItem.PartId != newItem.PartId || oldObj.VendorId != newObj.VendorId)
                             SetPoItemDefaultPartValues(newItem, PoParts, newObj.VendorId);
 
-                        continue;//on to next item
+                        continue;//Note: this accounts also for any change received quantities so no need to check that below
                     }
 
 
@@ -616,16 +617,18 @@ namespace AyaNova.Biz
                         if (newItem.QuantityReceived > 0 && newItem.ReceivedCost == 0 && newItem.PurchaseOrderCost != 0)
                             newItem.ReceivedCost = newItem.PurchaseOrderCost;
 
+                        //update serials if they have changed
+                        if (oldItem.Serials != newItem.Serials)
+                        {
+                            await PartBiz.RemoveSerialsAsync(oldItem.PartId, oldItem.Serials, ct, UserId);
+                            await PartBiz.AppendSerialsAsync(newItem.PartId, newItem.Serials, ct, UserId);
+                        }
+
                         continue;//on to next
                     }
 
+                    //### BEFORE ADDING MORE CHECKS HERE MAKE SURE LOGIC WORKS WITH ABOVE ###
 
-                    //CHANGED ONLY THE VENDOR
-                    if (oldObj.VendorId != newObj.VendorId)
-                    {
-                        SetPoItemDefaultPartValues(newItem, PoParts, newObj.VendorId);
-                        continue;//on to next
-                    }
                 }
             }//modified block
         }