circa Mon, 14 Jun 2004 22:08:11 -0400, in rec.pets.cats.health+behav,
Ruby Tuesday (willow93@yahoo.com) said,

A vet visit is in order. Bad breath can be caused by dental problems,
by excess stomach acid, by some cancers and myriad other things. In
all likelihood your cat just has stinky breath, but it's probably a
good time for him to have a checkup anyway. :-)

Laura

The first thing that comes to my mind, is that he may need dental work;
decay can smell pretty awful. ;-)

Vets often smell a cat's breath during a physical: different odors indicate
different conditions.  Anyway, if the stinky breath continues for a couple
of more days, I'd make a vet appt. for him.

Cathy

Ask your vet about dental exams and teeth cleanings, and about brushing your
kitty's teeth yourself. Why wouldn't her breath stink? Yours would if nobody
brushed your teeth.

This happened to our first cat and I thought it was normal but when I read
up on it I found that it's not.  When the Vet cked him out she found that 2
of his teeth were loose and that he had a medical ailment that he is
actually allergic to his own teeth.
She ended up doing a thorough cleaning and pulling the 2 loose teeth and
said eventually he might lose all of them.
That was 2 years ago and he no longer has bad breath and seems much happier.