can anyone help my chinchilla??

[ChickGirl6]

That sounds like ringworm. I'd go right away in the morning and get some antifungal cream to put on it.

 

[punk-a-doodle]

A vet can treat Ringworm, or you can as well. Whatever you are most comfortable with. Please do keep in mind that it can and will spread easily to humans and any other pets. It's very itchy and annoying to get rid of. Interestingly, some types will light up under a black light, which is one way to see if that is what is causing the bare patch:
http://good-times.webshots.com/photo/2046981240104536466ACPFmN
Here are some tips on treatments (I do not own chinchillas, and can not comment on their effectiveness or chin safety):
http://www.chinchillas.com/resource/fungus.htm
http://askville.amazon.com/Chinchil...in-pink-vet/AnswerViewer.do?requestId=2713789