 <p>I would do this in the <code>RowDataBound</code> event. </p> <pre><code>protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { var chk = e.Row.FindControl("CheckBox1") as CheckBox; if (chk != null) { var ddl = e.Row.FindControl("DropDownList1") as DropDownList; if (ddl != null) { //assign the JavaScript function to execute when the checkbox is clicked //pass in the checkbox element and the client id of the select chk.Attributes["onclick"] = string.Format("toggleSelectList(this, '{0}');", ddl.ClientID); } } } </code></pre> <p>The <code>toggleSelectList</code> function would look something like this:</p> <pre><code>toggleSelectList = function(el, selectID){ var selectElement = document.getElementById(selectID); if (selectElement){ selectElement.disabled = !el.checked; } } </code></pre>