Using this code you can shorten the time it takes to load a Combo Box. It works best when you're adding numbers (up to 3 times faster) or short strings (up to 2 times faster). Download the sample project to see for yourself.

Note: LB_ADDSTRING can be used in same way to add items to a List Box. But in the case of the List Box there is no speed increase.

Option Explicit

Private Const CB_ERR As Long = -1
Private Const CB_ADDSTRING As Long = &H143
Private Const CB_RESETCONTENT As Long = &H14B
Private Const CB_SETITEMDATA As Long = &H151

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _
hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Public Sub AddItem(cmb As ComboBox, Text As Variant, Optional ItemData As Long)

   Dim l As Long
   Dim s As String

   If VarType(Text) = vbString Then
      s = Text
   Else
      s = Trim$(Str$(Text))
   End If

   l = SendMessage(cmb.hwnd, CB_ADDSTRING, 0&, ByVal s)
   If l <> CB_ERR Then
      SendMessage cmb.hwnd, CB_SETITEMDATA, l, ByVal ItemData
   End If

End Sub

Public Sub Clear(cmb As ComboBox)

   SendMessage cmb.hwnd, CB_RESETCONTENT, 0, 0&

End Sub

  FastCombo.zip - contains: Fast Combo Sample Test (7 kb)