get two cotton swabs, soak one in a bit of rubbing alcohol and rub it over the scroll ball, make sure the ball has completely rotated in all directions. Then take the other cotton swab and do the same thing. This is for the first time, and then after this just periodically hold the mouse upside down, push down hard, and rotate in all directions with your fingers. This is what the mac Genius at the store I go to told me to do.