<% If rcount >  0  Then %> 
  var city_name = new Array(<%= ccount %>);
  var city_id = new Array(<%= ccount %>);
  var city_region_id = new Array(<%= ccount %>);
  city_num = <%= ccount %>
  
  city_name [0 ] =  "Другой населенный пункт" ;
  city_id [0 ] =  -99999 ;
  city_region_id [0 ] =  0 ;
  <% End If %>
  
  <asp:repeater id= "cityrepeater"  runat= "server"  enableviewstate= "false" >
    <itemtemplate>
      city_name[<%= cindex %>] =  "<%# DataBinder.Eval(Container.DataItem, " Name ") %>" ;
      city_id[<%= cindex %>] =  "<%# DataBinder.Eval(Container.DataItem, " ID ") %>" ;
      city_region_id[<%= cindex %>] =  "<%# DataBinder.Eval(Container.DataItem, " RegionID ") %>" ;
      <% cindex = cindex +  1  %>
    </itemtemplate>                                            
  </asp:repeater>
          
  <% If rcount >  0  Then %>          
  function regionchange() {
    var ptn2 = MainForm.<%= Replace(RegionList.UniqueID,  ":" ,  "_" ) %>;
    var txt = MainForm.<%= Replace(RegionName.UniqueID,  ":" ,  "_" ) %>;
    var ptn1 = MainForm.<%= Replace(CityList.UniqueID,  ":" ,  "_" ) %>;
    ptn1.options.length =  0 ;
    var optionName = new Option(city_name [0 ], city_id [0 ], false, false);
    ptn1.options[ptn1.length] = optionName;
    for (i =  0 ; i <= city_num; i++) {
      if (city_region_id == ptn2.options[ptn2.selectedIndex].value) {
        var optionName = new Option(city_name[i], city_id[i], false, false);
        ptn1.options[ptn1.length] = optionName;
      };
    };
    if (ptn1.length ==  1 ) {
      ptn1.options.length =  0 ;
      ptn1.disabled = true;
    } else {
      ptn1.disabled = false;
    };
    if ((ptn1.disabled == true) || (ptn2.selectedIndex ==  0 )) {
      txt.value =  "";
      txt.disabled = false;
    } else {
      txt.value = ptn2.options[ptn2.selectedIndex].text;
      txt.disabled = true;
    };
    <% If ccount > 0  Then %>
    citychange();
    <% End If %>
  };
  <% If ccount >  0  Then %>
  function citychange() {
    var ptn1 = MainForm.<%= Replace(CityList.UniqueID, ": ", " _ ") %>;
    var txt = MainForm.<%= Replace(AreaName.UniqueID, " : ", " _ ") %>;
    if ((ptn1.disabled == true) || (ptn1.selectedIndex == 0 )) {
      txt.value = " ";
      txt.disabled = false;
    } else {
      txt.value = ptn1.options[ptn1.selectedIndex].text;
      txt.disabled = true;
    };
  };
  <% End If %>
  regionchange();
  <% End If %>

-- естественно в vb есть такое:
 
      RegionList.Attributes.Add("OnChange ", " regionchange();")