どっちでも好きな方をどうぞ
samsu(cnt) = WorksheetFunction.Match(Cells(cnt, 1), Worksheets("ABC").Range(Worksheets("ABC").Cells(5, 2), Worksheets("ABC").Cells(400, 2)), 0)
samsu(cnt) = WorksheetFunction.Match(Cells(cnt, 1), Worksheets("ABC").Range("B5:B400"), 0)