Rats appearing in your dreams are a negative omen, exactly like the ugly, filthy animals. Most of the time the rats crawling in dark places in your dream represent degrading and shameful thoughts and feelings, your own remorses or feelings of guilt, things you have left unsolved and also envy.
Another pregnant characteristic of rats is their ugliness which gives birth to feelings of disgust and repulsion.
The rats in your dreams may be the image of your untrustworthy friends in waking life. Though you consider them close and true friends, they will eventually show their real intentions, which are linked to feeding off you and mischievously use you in their own interest. These animals are also connected with deceit and disappointment.
If in your dream you chase and manage to catch rats, this means that you criticize the vices, depravity and lack of morality of the others around you, but you fail to closely investigate your own.
A dream in which you kill mice bears a positive significance, announcing forthcoming success and fortune in your life. You succeeded in annihilating the bad luck, the 'filth' in your present life, therefore good times are just around the corner.
A white rat, though very rare in dreams, is a positive omen and announces unexpected help you will receive from a friend or someone else when going through rough times.
We should not forget that the rat is the carrier of plague, therefore its bite is extremely dangerous. Such rodents also destroy crops. In conclusion, rats in our dream may also be interpreted as a menace for our health, announcing health disorders in our waking life.
Rats may also appear in our dreams as sexual symbols, standing for our obsessive sexual desires, which we desperately want to repress when awake, but which come to haunt us in dreams at night, when we cannot control them. These obsessive sexual desires may refer to queer tendencies, such as voyeurism, homosexuality etc.
Also consult the MOUSE entry.