Private Sub UserForm_Initialize()
 Dim cell As Range

'Populate NIGO dropdown menu from "DropDownMenus worksheet.
 For Each cell In .Range("B2:B" & .Cells(Rows.Count, 2).End(xlUp).Row)
 If Not IsEmpty(cell) Then NIGOcombobox.AddItem cell.Value
 Next cell
 End With

Private Sub NIGOcombobox_Change()

 With Worksheets("DropDownMenus")
 .Activate
 Select Case NIGOcombobox
 'Populate NIGO Reason list by dropdown menu selection.
 Case "AMRF"
  For Each cell In .Range("C3:C" & .Cells(Rows.Count, 3).End(xlUp).Row)
  If Not IsEmpty(cell) Then ListBox1.AddItem cell.Value
 Next cell

 Case "OATS"
  For Each cell In .Range("D3:C" & .Cells(Rows.Count, 3).End(xlUp).Row)
  If Not IsEmpty(cell) Then ListBox1.AddItem cell.Value
 Next cell

 Case Else
  MsgBox "Please select a NIGO Reason"

 End Select
 End With
 End Sub