Sorry, I should have been more explicit:
Function AddNumbersInListbox(ListboxControl As Listbox) As xxxx
Dim lngLoop As Long
Dim lngSum As xxxx
lngSum = 0
For lngLoop = 0 To (ListboxControl.ListCount - 1)
lngSum = lngSum + ListboxControl.ItemData(lngLoop)
Next lngLoop
AddNumbersInListbox = lngSum
End Function
Change xxxx to the appropriate data type (Single, Double. Decimal, Currency,
whatever's appropriate for the data)