Hvorfor virker den Replace her ikke?

Dim SearchString As String = Replace(Request.QueryString("keyword", "'", "''"))

        Dim strSQL As String = "SELECT VareId, Varenr, Varenavn, Farve, Materiale, Specs, Pris, Leverandør FROM Vare "
        strSQL += "WHERE VareId LIKE '%" & SearchString & "%'"
        strSQL += "OR Varenr LIKE '%" & SearchString & "%'"

For følgende fejl:

Name 'Replace' is not declared.

Source Error:
Line 37:        objConnection.Open()
Line 38:
Line 39:        Dim SearchString As String = Replace(Request.QueryString("keyword", "'", "''"))