Pam, the cat could have any number of issues- the scariest of all would be something as severe as rabies. However, he would not live very long if that were the case. Just in case, do not handle him or his saliva. I know it sounds far-fetched, but without a better description from you, I would rather warn you of the worst case scenario... other more likely problems could be oral infection or tumor that is keeping him from being able to close his mouth and is causing difficulty swallowing. Sometimes cats will drool due to nausea and believe it or not, some drool when they are happy or nervous. Can you give us a more detailed image so we can be more helpful? Thanks for helping a stray animal!