How to introduce adult (female) cats.

[purplelollypop]

I have 2 adult female cats and have just adopted another adult,also female. So far I have kept the old 2 and the new one apart but just wondering if anyone has and experience or advce as to how to go about introducing them. The old 2 can be very hostile towards other cats they have met. Is it best to just let them get on with it (I'm worried for the safety of the new one!) or is there a way of doing it slowly? Also worried one or both of the old cats will decide to leave home when they discover the new addition!

Have never introduced an adult to an older cat but when we had our new kittens we let them 'experience' each other from either side of the glass door. We also 'shared their scent' using towels etc so that the new kittens smelt a little of the old cat after being rubbed in his towel.

It might be different with introducing an older cat