Userform_initialize - Reset A Form

I have created a form containing a list box. This list box contains values (Items) that correspond to a particular product (i.e. each time I view a new product, I need to see a new list of items in the list box). I have used Userform_initialize to set the Items (see below). The values are themselves drawn from a spreadsheet. I have only pasted the piece of code in question - I have a lot more code prior to that in order to define the variable "varcount".

Userform_initialize
Dim w As Workbook
Dim varLine As Integer
Dim varcount As Integer
Dim vItem As String
Set w = ThisWorkbook
For counter = 1 To varcount
Selection. Offset(0, 0).Select
vItem = Selection.Value
frmCheckTwinSku.lbTwinSku.AddItem (vItem)
Selection.Offset(0, 1).Select
Next counter.........................