This article is from the Chihuahua Breed FAQ, by firstname.lastname@example.org (Melinda 'Bob' Casino) with numerous contributions by others.
Not much. This little breed has bouts of energy each day which
quickly die down. They have been known to play catch with small
balls, if taught at an early age. Much of their exercise, though, is
fulfilled by pattering around the household following their master,
or playing with their toys (old slippers are ideal, as well as wooly
stuffed toys with squeakers inside.)
You can certainly take this breed on walks. You will gain much
attention and make many an acquaintance due to the diminutive and
unusual appearance of your Chihuahua.
When buying a leash for your Chihuahua, remember that its neck is
rather small and delicate compared to other dog's necks. You cannot
(and, indeed, should not) yank your dog around by the leash if s/he
has a neck collar on. And choke chains should definitely NOT be used
on Chihuahuas! I recommend the body-harness. If fitted right, it will
give your Chi a secure and comfortable walk (see photo).
The body harness goes over the head of the dog and buckles under the
torso in an H-design. I highly recommend these for Chihuahuas, since
they ensure that your dog cannot escape (a real concern if you live
in an urban area) and don't have the potential to harm the dog like