SlideDown/SlideUp menu

SlideDown/SlideUp menu

hi, i m new in JQuery, i m try to use Jqeury to make a slidedown menu , the html code like below:

<ul>
   <li>
      <a href="#">item</a>
        <span>
           <a href="#">subitem</a>
        </span>
   </li>
</ul>

i hope when mouse over the <li> item, will show the "subitem", i use slideDown done it well,
but how to make it SlideUp when mouseout?