My rat is sneezing a bit, but he's healthy other than that. He tends to do it when i let him run around, or he gets excited. do u think its resperatory desease or do they do that as a show of excitment?

It could be a number of things, The bedding he lives on could be very dusty, something could be dusty or annoying his nose when you let him out. Sometimes Naz will get into corners of moms shelves when we're in the living room and since they are a little dusy he'll sneez once to twice. So it could be just a dust or other moment seenzeing issues.
Then it also COULD be he's sick and has a Resp. infection. Is there anything else you can tell us? what type of bedding he lives on? how often you clean his cage?? He could have allergys and the list goes on.

i've got an aspen wood shavings bedding. i just got him about two weeks ago and i've cleaned it once since then--he lives alone but i'm most definitly planning to get another one.

I've not seen them sneeze out of excitement before, but they can often sneeze a lot when they are taking in lots of new smells, ie when you let him run around places etc.

I've not seen them sneeze out of excitement before, but they can often sneeze a lot when they are taking in lots of new smells, ie when you let him run around places etc.that could be it....i just got him, so maybe he's just, like you said, "taking in lots of new smells"

Just keep your eye on it and if it carries on for too long or gets worse in any way (laboured breathing, lots of porphyrin etc), have a vet look him over. I imagine he'll get over it soon, though. :)

also, he sneezes when i pick him up or put him back in the cage. could this possibly be a sign of distress?

It is possible, I guess, but I've not heard of that before. I'm sorry, I'm not much help on this one. Perhaps someone else will be able to help a bit better on this one.