mouse wheel only scrolls down, not up

Clean it as described in http://support.apple.com/kb/ta26691

If it's a Mighty Mouse with the little ball on top (not the type described in the post above) you can try disconnecting the mouse, turn it upside down, press down gently and roll around a good bit on a piece of regular white printer paper.

If you are using a Mighty Mouse, turn it upside down and vigorously roll it on a sheet of white paper or clean lint free cloth.

see > http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT3226/HT326.mov

If that doesn't help, try a few drops of Isopropyl alcohol on your cloth or an Isopropyl wipe to clean the ball and then blow around the ball with compressed or canned air.

Thanks for jumping in. I didn't check the article closely enough to see that it was about the older mouse. For the OP, see https://discussions.apple.com/thread/1262339?start=0&tstart=0 and http://www.google.co.jp/search?client=safari&rls=en&q=clean+mighty+mouse&ie=UTF- 8&oe=UTF-8&redir_esc=&ei=GotkTdz1HImecL_c5dgF

This happens to me in Safari sometimes (Mac OS X 10.8.5 / Apple Mouse / plain wired usb mouse / Safari 6.0.5).

The fix is to switch to another application temporarily,

such asTerminal.app or Firefox.app.

Then excercise the wheel up in the other app..

notice the wheel-up action scrolls properly..

Then switch back to Safari..

and it should work properly again for a few weeks

(without rebooting)..