Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim rang As Byte, longueur As Byte
longueur = Len(Range("B25"))
Range("B25").Characters(1, longueur).Font.Underline = xlUnderlineStyleNone
longueur = Len(Range("D27"))
rang = InStr(UCase(Cells(25, 2)), UCase(Cells(27, 4)))
Range("B25").Characters(rang, longueur).Font.Underline = xlUnderlineStyleSingle
End Sub