Ajax (3) ajaxToolkit

<asp:UpdatePanel ID="UpdatePanel1" runat="server">

<ContentTemplate>

<asp:TextBox ID="SearchText" runat="server" />

<ajaxToolkit:AutoCompleteExtender runat="server" ID="AutoCompleteSearch"

MinimumPrefixLength="1" TargetControlID="SearchText"

ServicePath="AutoCompleteService.asmx"

ServiceMethod="GetSearchTerms">

</ajaxToolkit:AutoCompleteExtender>

</ContentTemplate>

</asp:UpdatePanel>