or
<telerik:RadPanelBar ID="RadPanelBar1" runat="server" Height="300px" onitemclick="RadPanelBar1_ItemClick" Skin="Office2007" ValidationGroup="MenuOptions" Width="180px">function RadComboBoxKeyPressing(combo, eventArgs) { var key = eventArgs.get_domEvent().keyCode; var allow = decOnlyKey(key, combo.get_text());// if (!allow)// eventArgs.set_cancel(true);}<tr id="trForwardEmail" runat="server"> <td> Forward Email To: </td> <td width="10"> </td> <td> <telerik:RadComboBox ID="cmboForwardEmail" runat="server" width="200" OnClientSelectedIndexChanging="ShowCheckbox"/> </td> </tr>function ShowCheckbox(sender, eventArgs) { var checkbox = document.getElementById("<%= trSaveEmail.ClientID %>"); var cmboBox = $find("<%= cmboForwardEmail.ClientID %>"); alert(cmboBox.get_text()); if(cmboBox.get_selectedItem().get_text() != "No Forwarder") { checkbox.style.visibility = "hidden"; } else { checkbox.style.visibility = "visible"; }}