Introducing rats to other rats

Question
We've had 2 female pet rats for about 4 months now. They seem happy and
healthy and they get along well, but one is extremely shy and sleepy, the
other is more adventurous and hankers after attention (by chasing me around
the kitchen!) when her friend is sleeping and doesn't want to wake up. We'd
like to get another 2 female rats so she has plenty of friends to play with.
What is the best way to go about introducing them?

Answer
Very rarely do I have issues introducing my ratties to new ratties -- but to be on the safe side, after you quarantine your new rats (for a minimal 2 weeks in separate airspace), introduce them in a neutral territory (such as the sofa, or the empty bathtub) while you completely clean out and sanitize the cage everyone will be living in together. After you've sanitized the cage and its contents completely, you can see how the girls are getting along and put them together in the cage if everyone seems content. There will probably be squeaking, and some dominant females flipping the others onto their back and "acting" aggressive and puffy, but the rule with rats is NO BLOOD, NO FOUL. Don't separate them during this time, as it will only make it worse. If someone is injured, obviously you do need to separate them.. otherwise, let them work it out.

Good luck!