 <p>I think you may combine following examples:</p> <ol> <li><p>Load on demand: <a href="https://demos.telerik.com/aspnet-ajax/combobox/examples/loadondemand/wcf/defaultcs.aspx" rel="nofollow">https://demos.telerik.com/aspnet-ajax/combobox/examples/loadondemand/wcf/defaultcs.aspx</a></p></li> <li><p>Related combo boxes: <a href="https://demos.telerik.com/aspnet-ajax/combobox/examples/functionality/multiplecomboboxes/defaultcs.aspx" rel="nofollow">https://demos.telerik.com/aspnet-ajax/combobox/examples/functionality/multiplecomboboxes/defaultcs.aspx</a></p></li> <li><p>Overview: <a href="http://www.telerik.com/help/aspnet-ajax/combo_loadondemandoverview.html" rel="nofollow">http://www.telerik.com/help/aspnet-ajax/combo_loadondemandoverview.html</a></p></li> </ol>