function showdept()
  {
Listdepnum()//这样调用行吗？
}

DropDownList3.Attributes.Add("onClick", "showdept()")

<Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)> _
    Private Sub Listdepnum() '顯示部門
        If DropDownList2.SelectedIndex <> -1 Then
            Dim strSQL As String
            Dim dsResult As New DataSet
            Dim clsDBProcess As New dbprocess.OledbProcess
      strSQL = "select dept_num,dept_nam from DEPT where fac_num='" & DropDownList2.SelectedValue & "'"
            dsResult = clsDBProcess.GetDataSet(Session("Server"), Session("Database"), strSQL)
            DropDownList3.DataSource = dsResult
            DropDownList3.DataTextField = "dept_nam"
            DropDownList3.DataValueField = "dept_num"
            DropDownList3.DataBind()
            DropDownList3.Items.Insert(0, New ListItem("请选择", " "))
        End If
    End Sub

以下是其它类同的调用例子
                 function Validata()
            {
         ClassesMaint.Listde(document.all.txtClsnum.value,Validata_Result_CallBack);
            }
           
            function Validata_Result_CallBack(response)
            {
                if (response.value != null)
                {                    　　　            
　　　　            var ds = response.value;
                    if(ds != null && typeof(ds) == "object" && ds.tables != null)
                    {           
             for(var i=0; i<ds.tables[0].Rows.length; i++)
　　　　                {
　　　　　　                 document.all.txtCrsnum.value=ds.tables[0].Rows[0].emp_chn_nam;
　　　　　　                return;
　　　　　　            }
                    }
                }                
                return
            }            

<Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)> _ 
    'Private Sub Listdep(ByVal DropDownList2) '顯示部門 
'=======>
public function Listdep(ByVal DropDownList2) '顯示部門 

        Dim strSQL As String 
        Dim dsResult As New DataSet 
        Dim clsDBProcess As New dbprocess.OledbProcess 
        strSQL = "s