<script language = "javascript"> function checkedPoC( _obj ){ if( _obj.checked ){ document.Form1.txtPoC.disabled = true; }else{ document.Form1.txtPoC.disabled = false; } }</script><form name = 'Form1'> Estado: <input type = 'checkbox' id = 'checkPoC' name = 'checkPoC' onClick='javascript:checkedPoC(this);'> <input type = 'text' id = 'txtPoC' name = 'txtPoC'></form>