Instructions
Introducing a New Cat to the Resident Cats
Establish the new cat's room in an area that the other cats are not allowed into. Keep the new cat's food, water, litter box, and other materials in this room.
Bring objects that have the new cat's smell on them, such as toys or a towel, to the established cats and allow each cat to get used to the newcomer's scent. Bring objects with the scent of the established cats to the newcomer, as well, and repeat the process regularly.
Take the established cats and put them in the newcomer's room, and allow the new cat to explore your home without the other pets interfering.
Place the new cat's food near to the door of its room, and place the established cats' food near to the door on the other side; this allows the cats to associate something pleasurable with each other's scents. Gradually bring the dishes closer to the door if they do not show discomfort.
Allow the cats to be in the same room under close supervision. Expect growling and hissing, and be ready to stop the cats if fighting occurs. Separate them if either is excessively aggressive or afraid. Use a water pistol or throw a large pillow nearby to stop the cats if actual fighting occurs. Repeat these interactions daily, increasing or decreasing interaction time based on their behavior.
Allow unsupervised interaction after several consecutive sessions without overly aggressive behavior.
How to Introduce a Siamese to Other Cats
Siamese cats are regarded as intelligent, social, and affectionate pets, and they make a welcome addition to most households. However, while the Siamese is not unusually aggressive or territorial, all domestic cats retain a degree of their wild roots, and the introduction of a new cat to a household can be a trying ordeal for both the newcomer and established residents. Some care must be taken to keep the cats from fighting and acclimate them to each other.