<asp:ScriptManager ID="asm" runat="server" /> 

<div>      
	Vendor: <asp:DropDownList ID="VendorsList" runat="server" /> 
</div>

<ajaxToolkit:CascadingDropDown ID="ccd1" runat="server"      
	ServicePath="CascadingDropdown0.cs.asmx" ServiceMethod="GetVendors"      
	TargetControlID="VendorsList" Category="Vendor" /> 

public CascadingDropDownNameValue[] MethodNameHere(string knownCategoryValues,      string category) 

<%@ WebService Language="C#" Class="CascadingDropdown0" %> 
using System.Web.Script.Services; 
using AjaxControlToolkit; 
using System; using System.Web; 
using System.Web.Services; 
using System.Web.Services.Protocols; 
using System.Collections.Generic; 

[ScriptService] public class CascadingDropdown0 : System.Web.Services.WebService 
{      
	[WebMethod]      
	public CascadingDropDownNameValue[] GetVendors(string knownCategoryValues, string category)      
	{           
		List<CascadingDropDownNameValue> l = new List<CascadingDropDownNameValue>();           
		l.Add(new CascadingDropDownNameValue("International", "1"));           
		l.Add(new CascadingDropDownNameValue("Electronic Bike Repairs & Supplies", "2"));           
		l.Add(new CascadingDropDownNameValue("Premier Sport, Inc.", "3"));           
		return l.ToArray();      
	} 
}