how to insert list item in run time

Hi masters

i have one dropdownlist . This is getting data from databse at runtime. i have to insert <asp:ListItem><---Select Category From Below List---></asp:ListItem> . but this is not displaying on page load. so how to acheive it.

<tr><td height="24" align="left" class="style5">&nbsp; Letter To</td><td height="24" colspan="3" align="left">&nbsp;<asp:DropDownList ID="txother_details" runat="server" CssClass="tx" Width="396px" AutoPostBack="true"></asp:DropDownList></td></tr>