Suddenly, without warning, blkcatgal exclaimed (11/12/2007 7:40 AM):

See a vet.  There's one thing you can check though.  Have a close look
at the fur that is still there.  Is it rough, chopped off short, or does
it come to a natural point?

If it's short, then your cat's doing the same thing Meep is:  fur
mowing.  We haven't diagnosed Meep's problem yet, she was put on a
long-acting antibiotic but there result was inconclusive.  We know she
licks at it, but only when I'm not looking, so the suspicion is
behavioral.  Got Feliway, been about a month, but so far no change.

Watch her when she grooms.  Does she spend more time on her belly?  Is
she biting at the fur there, or otherwise grooming it differently than
the rest of her body?  The vet might ask this...

Any environmental changes, changes in the household routine, changes in
her food?  All clues for the vet to figure out what's wrong.

Take her to the vet, and let us know what the vet says.

jmc