jquery fadeIn not working

Can someone please tell me what I'm doing wrong:

style:

.warning{border: 1px solid #F0AAAA; background:#FFBABA; color: #C90000;}

markup:

 <p class="warning">A successful authorization already exists. 
                    Further authorizations are not allowed at this time.</p>

script:

 $().ready(function () {
     alert($(".warning").html());     // WORKS
     $(".warning").fadeIn(4000);      // DOESN'T WORK
 });