How to set selected Items in listbox to none?

Hi there, just a quick one this, the title probably explains my question sufficiently, I just want to deselect everything in a listbox. I have tried:
[AS]
myList_list.selectedItem = null;
myList_list.selectedItem = undefined;[/AS]
but it wont work.

Would someone let me know the correct syntax pls?
Thanks,

Schm