Consider a GridView that contains three columns: First Name, Alien Dropdown and Country Dropdown. The Alien Dropdown has two options, Yes and No. Select Yes in the Alien Dropdown. The Country Dropdown is enabled.

Both Dropdowns are defined in a TemplateColumn. For this example, we bind the GridView to a XmlDataSource.

<asp:Gridview ID="Grid1" runat="server" 
DataSourceID="NameXml" 
AutoGenerateColumns="false"
OnRowDataBound = "Grid1_RowDataBound" >
<Columns>
<asp:BoundField DataField="FirstName" />
<asp:TemplateField>
    <ItemTemplate>
        <asp:DropDownList ID="AlienList" runat="server" 
        AutoPostBack="true"
        OnSelectedIndexChanged="AlienList_SelectedIndexChanged" >
            <asp:ListItem Text="Yes" Value="Y"></asp:ListItem>
            <asp:ListItem Text="No" Value="N"></asp:ListItem>
        </asp:DropDownList>
    </ItemTemplate>
</asp:TemplateField>
<asp:TemplateField>
    <ItemTemplate>
        <asp:DropDownList ID="CountryList" runat="server">
            <asp:ListItem Text="" Value=""></asp:ListItem>
            <asp:ListItem Text="USA" Value="USA"></asp:ListItem>
            <asp:ListItem Text="UK" Value="UK"></asp:ListItem>
        </asp:DropDownList>
    </ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:Gridview>
<asp:XmlDataSource ID="NameXml" runat="server" DataFile="Names.xml">
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