Option Explicit
Private Sub UserForm_Initialize()
Dim r As Long
ComboBox1.ColumnCount = 2
For r = 1 To Range("A" & Rows.Count).End(xlUp).Row
ComboBox1.AddItem Range("A" & r).Value
ComboBox1.List(r - 1, 1) = r
Next
End Sub
Private Sub ComboBox1_Change()
Dim r As Long
Dim c As Integer
r = ComboBox1.List(ComboBox1.ListIndex, 1)
ComboBox2.Clear
For c = 2 To Cells(r, Columns.Count).End(xlToLeft).Column
ComboBox2.AddItem Cells(r, c).Value
Next
End Sub