Some cats just don't like other cats.  Same as people.  I have 25.

My oldest is a 16-year old calico who is reclusive and does not get along
with the younger, newer feline residents in the house.  Two years ago I put
her in my office with another younger female who is likewise a recluse; and
to this day the two of them separate themselves by as much space as the 12 X
16 room will allow.  They do not fight, but are both fiercely (hissively)
protective of their own precious areas of possession.  The room's size and
ample window space seems to satisfy each cat's needs, as socialization is
not one of them.

In your case, I suggest you give the cats as much room as possible and let
dominance prevail.  Although there *are* exceptions, cats seldom injure one
another in territorial disputes (unless breeding rights are challenged--as
the weaker will seek an exit, and the aggressor will usually only pursue
long enough to firmly establish dominance.

In fact, often until that point is settled, the two will posture like
schoolyard bullies during recess.  I have learned not to intervene when a
ruckus starts--unless it appears that severe damage is imminent--but to let
them work it out.  It may take a while; and then it may be over in the blink
of an eye.  Following that, toleration may be the best you can expect.

--Geno<new here also>Royer
www.churchboardleadership.com
www.integrisdream.com/Generoyer

Make them smell the same with some tuna brine. Cats work on smells so
generaly the intolerance with a newcomer occurs cos they smell different
therefore like an intruder on the territory. Wipe some brine on their coats,
and I'd say opposite to previous poster, keep them in the same room. With
some luck they might lick each other off.

Also, feed them together and nearby. Give them treats only when they are in
the same room. Play with them only when they are together in the room. Let
them create some positive associations when other cat is around. Eventually
they will establish who's the boss and the other will be happy being second
in command.  They might never love each other, but will learn to tolerate.

Gee

Cats can be very odd about new cats in the house.  We had a male cat
and a female, neutered of cource, that we raised from kittens.   The
male, Bobby, died.   The female, Pasha, pined for at least six months.
 We got a female kitten to keep her company.  Two years on, they
still hate each other.   They don't often fight, and somotimes they
sit together, but they don't tolerate company at the food bowls, and
Pasha won't let the other, Susie, sit on my bed.

In my parents' case, 8 years and counting. The two have never, ever got
on!

We had a white cat called Lulu, our tardiness in getting Lulu spayed meant
we had 4 kittens. We kept one, a long-haired black kitten called Beth.
They were very close, ate together, slept together, played together, all
the rest of it.

Lulu died aged 6 we got another tortoiseshell kitten to keep Beth company,
called officially Cleopatra and in practice invariably "The Little Cat".

The assumption was that, because Beth and Lulu were so close, and Beth
was missing Lulu so much, that a kitten would cheer her up.

We were very, very wrong. They loathe each other to this day. They rarely
actually notice each other, pretending not to see another cat there, but
if unexpectedly face to face, hiss at each other and run off.

Amanda