Is possible select multivalue from DropDownList ????

i have DropDownList with sql select commend
<asp:DropDownList ID="DropDownList1" runat="server"
        DataSourceID="SqlDataSource_department" DataTextField="Department"
        DataValueField="Department_No" AutoPostBack="True"
        onselectedindexchanged="DropDownList1_SelectedIndexChanged">
    </asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource_department" runat="server"
        ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
        SelectCommand="SELECT [Department_No], [Department], [Code] FROM [Departments]">
    </asp:SqlDataSource>
in the behind ...