This example shows how to implement related comboboxes using Telerik ComboBox for ASP.NET MVC.

Use the ComboBox CascadeTo() method to set the ID of the related combobox.

<%= Html.Telerik().ComboBox()
        .Name("ComboBox1")
        .CascadeTo("ComboBox2")
%>
<%= Html.Telerik().ComboBox()
        .Name("ComboBox2")
        .DataBinding(binding => binding.Ajax().Select("_GetItems", "Home"))
%>

The second combobox ("ComboBox2") in this case will be disabled. Once you select a value from the first combobox ("ComboBox1") the second one will be enabled and populated.

If the second combobox uses "load on demand" binding then an Ajax request will be made passing the selected value of the "ComboBox1". Here how the Action method should look like:

public JsonResult _GetItems(string ComboBox1) 
{
    // use the value of the ComboBox1 to filter the data

    //return List as JSON
}