Dim Wb As Workbook
Dim Ws As Worksheet
Dim x As Variant
Dim MaDate As Date
On Error Resume Next
'MaDate = InputBox("Saisissez une date.", Title:="Recherche d'une Date")
'If MaDate = 0 Then Exit Sub
MaDate = "01/01/10"
For Each Wb In Application.Workbooks
For Each Ws In Wb.Worksheets
For Each x In ThisWorkbook
Set x = Ws.Cells.Find(MaDate)
If Not x Is Nothing Then
x.Offset(0, 1).Value = 1
End If
Next x
Next Ws
Next Wb