It is more troublesome to use asp. Every change has to be submitted and returned, so it is usually implemented with javascript...

< script language="javascript">

var d=document.getElementById;

var arr1=new Array();

var arr2=new Array() ;

var i=0;

arr1[i++]="a";

arr1[i++]="b";

i=0;

arr2[i++]=new Array("a1","a2","a3");

arr2[i++]=new Array("b1","b2","b3");

arr2[i++]=new Array("c1","c2" ,"c3");

function change(){

var id=d("a").selectedIndex;

d("b") .options.length=arr2[id].length;

for(var i=0;i

d("b" ).options[i]=new Option(arr2[id][i],i);

}

d("b").selectedIndex=0;

}

function initialize(){

d("a").options.length=arr1.length;

for(var i =0;i

d("a").options[i]=new Option(arr1[i],i);

}

d("a").selectedIndex=0;

change();

}

initialize();

p>

When using it, just load the large class and the small class into the two arrays arr1 and arr2 respectively..^_^..