Sub test()
Application.ScreenUpdating = False
Dim rng As Range
For i& = 2 To Me.Cells(1, Columns.Count).End(xlToLeft).Column
Set rng = Me.Range(Me.Cells(2, i), Me.Cells(Me.Cells(Rows.Count, 1).End(xlUp).Row, i))
rng.SpecialCells(xlCellTypeBlanks) = Cells(1, i)
Next
Application.ScreenUpdating = True
End Sub