Jquery slide

Jquery slide

Hi,
 
I have data coming from a DB and, for each row called, I have a sub nav that is hidden. Clicking on a link will toggle the menu down.
 
I am using;
 
$(
this ).parent().find( "ul.subnav" ).slideToggle( 'medium' );
 
Which in essence works, i.e. when I click the selected row it drops down and when I click again it closes. Trouble is if I leave it open and click the next row, I get two open and so on.
 
I want all to close other then the one I have clicked to open!
 
Any help would be apprecied.
 
Cheers folks.