Sub essai()
If ActiveSheet.Range("A18").Value<> "" Then
' code si A18 non vide
ElseIf ActiveSheet.Range("A19").Value<> "" Then
' code si A19 non vide
ElseIf ActiveSheet.Range("A20").Value<> "" Then
' code si A20 non vide
Else
Exit Sub ' On sort si les trois cellules sont vides
End If
End Sub