Sub test()
Dim cellFind As Range, cellSearch As Range
Set cellSearch = ThisWorkbook.Sheets("CASE_A_COCHER").Range("A2")
While cellSearch.Text <> vbNullString
Set cellFind = ThisWorkbook.Sheets("LISTE").Range("A:A").Find(cellSearch.Value, , xlValues, xlWhole)
If Not cellFind Is Nothing Then cellFind.Offset(0, 1).Value = "OK"
Set cellSearch = cellSearch.Offset(1, 0)
Wend
End Sub