Datagridview

[dglienna]

You'll need to skip line 0, then start comparing ircNo+1 to ircNo each time, unless it's an odd number of items. Might need another condition to handle that

    If e.Button Is ToolBarButton1 Then
    Dim irowNo As Integer, OldValue as String
      For irowNo = 0 To DgvPracExcl.Rows.Count - 1
        if rowNo = 0 Then 
           oldValue = "None"
        else
           oldValue = oldValue
        End If
        If DgvPracExcl.Rows(irowNo).Cells(2).ToString() = "old" Then ' or the correct string to compare?
            oldValue = DgvPracExcl.Rows(irowNo).Cells(2).ToString() 
        End If
       ' Now compare
       If DgvPracExcl.Rows(irowNo).Cells(2).ToString() = oldValue
               DgvPracExcl.Rows(irowNo).Cells(3).ReadOnly = True
       Else
                DgvPracExcl.Rows(irowNo).Cells(3).ReadOnly = False
       End If
   Next irowNo

Free-hand...