Chas

You don't say how you are accessing the Access database, so I'll use the
Data Object.

I will assume that Combo1 holds a list of unique items that can reliably be
used for a search.

Private Sub Combo1_Click()
    Dim criteria As String

    criteria = "MyField = '" & Combo1.Text & "'"    ' note:  Single quotes
used for text. If numeric, then no single-quotes.

    Combo2.Clear

    Data1.Recordset.FindFirst criteria

    Do Until Data1.Recordset.NoMatch = True
        Combo2.AddItem Data1.Recordset.Fields("MyField")
        Data1.Recordset.FindNext criteria
    Loop
End Sub

If your list might have duplicate entries in Combo1 and thus be prone to
search errors on the text, you might look into the ItemData property of
ComboBoxes and ListBoxes.  It is a Long Integer that is associated with each
item in the list.  If, when you fill Combo1, you also add a Long primary key
(such as an Autonumber) to the item's ItemData then each item will have a
unique identifier for searching.

Private Sub Combo1_Click()
    Dim criteria As String

    criteria = "MyNumericField = " & Combo1.ItemData(Combo1.ListIndex)

    Combo2.Clear

    Data1.Recordset.FindFirst criteria

    Do Until Data1.Recordset.NoMatch = True
        Combo2.AddItem Data1.Recordset.Fields("MyField")
        Data1.Recordset.FindNext criteria
    Loop
End Sub

I hope that this helps.  If not, post again.

Michael