Javascript - Make A Select Option Change Options In Another Select?

I have two drop down. SelCurrentManuf and selCurrentModel. I want the option in selCurrentModel to change depending on the option selected in selCurrentManuf. How do i do it?

<asp:DropDownList runat="server" ID="selCurrentManuf"></asp:DropDownList>
<asp:DropDownList runat="server" ID="selCurrentModel"></asp:DropDownList>

This is how i am currently populating selCurrentModel

Public Sub PopulateCurrentModel()
Dim mySelectQuery As String = "SELECT * FROM Model where ManufID = "+ selCurrentManuf.Text+";"
Dim myConnection As New MySqlConnection(Session("localConn"))

[Code]...

but it only populates the first selected manuf, and doesnt change after

Private Sub selCurrentManuf_SelectedIndexChanged(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles selCurrentManuf.SelectedIndexChanged
PopulateCurrentModel()
End Sub