delete selected items from list ?

hi

i'm using one of select list and one button, for removing selected items from the list ?
this is a javascript which one i'm using..for deleting but its not working ?

function deleteSelectedItemsFromList(filterchain) {
var maxCnt = filterchain.options.length;
alert("*****"+"maxCnt="+maxCnt);
for(var i = maxCnt - 1; i >= 0; i--) {
if ((filterchain.options[i] != null) && (filterchain.options[i].selected == true)) {
filterchain.options[i] = null;
      }
   }
}

this is select list: once i clarify that ,i'm getting some of value in select list from my data only...
and i  want to delete items which ever i'l selected..

<select name="filterchain" size="10" id="filterchain">
<option value="timefilter">Time Filter</option>
<%
    FilterChainUtility filterChainUtility = FilterChainUtility.instance();
    Vector time = filterChainUtility.getTimeFilter();
    Iterator timeiter = time.iterator();
    while(timeiter.hasNext()){
        TimeFilterVO timeFilterVO = (TimeFilterVO) timeiter.next();
%>
<option><%=timeFilterVO.getFilterLabel()%></option>
<%
    }

%>
<option value="processfilter">Process Filter</option>
<%
    Vector process = filterChainUtility.getProcessFilter();
    Iterator processiter = process.iterator();
    while(processiter.hasNext()){
        ProcessFilterVO processFilterVo = (ProcessFilterVO) processiter.next();
%>
<option><%=processFilterVo.getFilterLabel()%></option>
<%
    }

%>
<option value="messagefilter">Message Filter</option>
<%
    Vector message = filterChainUtility.getMessageFilter();
    Iterator messageiter = message.iterator();
    while(messageiter.hasNext()){
        MessageFilterVO messageFilterVO = (MessageFilterVO) messageiter.next();
%>
<option><%=messageFilterVO.getFilterLabel()%></option>
<%
    }

%>

</select>

i dont know whats wrong with this ?
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