function chgOpts(lvl)
{
    switch (lvl)
    {
        case 2:
            var level = document.forms.immoform.Stadt;
            var parent = document.forms.immoform.Kreis;
            break;
        case 3:
            var level = document.forms.immoform.Ort;
            var parent = document.forms.immoform.Stadt;
            break;
        default:
        // void
    }

    for (i = level.length; i > 0; i--)
    {
        level[i]=null;
    }

    var opt = new Option("alle","");
    level.options[0] = opt;

    var wert = parent[parent.selectedIndex].value;

    if (wert)
    {
        var arr = ebene[lvl][wert];
        if (arr)
        {
            var ln = arr.length;

            for (i=0; i < ln; i+=2)
            {
                optvalue = arr[i];
                optname = arr[i] + " (" + arr[i+1] + ")";
                var opt = new Option(optname, optvalue);
                level.options[level.options.length] = opt;
            }
        }
    }

    level.selectedIndex = 0;
    
    return;
}