Problems with GetMouse; how to know when button is released

I am working with GetMouse and it seems the buttons returns 1 when
it is pressed once only. The documentation gives me the impression
that as long as keep the button down it should keep returning 1.
But, it returns 1 only the first time, and then returns 0 for every
GetMouse call afterwards.

Anyways, if this what it was meant to work as, then how do I get
that the mouse button has been released?

Thanks.