both of them have been spayed. if it makes a difference, zoey was spayed when she was a kitten and katie was spayed as a younger kitten. zoey is about 4 years old and katie is only about 2. we kept zoey and katie in the house each while they were kittens. when we got katie we kept her upstairs at night and zoey downstairs, but it really didn't seem to make a difference because we kept them both downstaires during the day and zoey didn't seem to mind. all the fighting just started about 4 months ago. still