Why would a healthy cat start sneezing and have a runny eye right after you adopted him?

This could be an upper respiratory infection, which is airborn (contagious), and that is probebly why this cat has caught it (from your other cat). You should get it into the vet for treatment, as you do not need a secondary infection on your hands. Keep it dry and warm and do not let it or outdoors with any other animals. Make sure you provide clean separate feeding bowls, clean bedding, etc., for both felines. Keep the separated, until you can get it in for treatment. Try a humidifier in a separate room for the feline such as a spare bedroom or steam from the shower in the bath room. The end result is you have to get this cat to your vet for treatment, otherwise you are looking at a vicious circle of U.R.I.'s * The above statement is partially true in saying that it could be an upper respitory infection and that it is airborne and contagious. The suggestions as to what you can do for the animal until you are able to get it to a vet to be checked are also good ones. However, I would like to say that depending on how long you have had the cat for often determines where the animal became sick and/or how long it has been sick for.. It is not uncommon for a pet to show symptoms of being sick within 2 weeks{ the average incubation period for most illnesses} of leaving a shelter setting.. Their immune systems are often compromised because of the stress they are under during the duration of their stay that when they are brought home and exposed to fresh air it can aggrivate and already exisiting problem. Check with the organization you adopted the animal from. They often have some sort of health warranty that covers the pet for a period of time after adoption that may help cover the cost of vet bills. Again, please be sure to get the little guy to a vet ASAP... Kechara Well it could be the change in environment or what is stated above. You should really get in touch withyour vet regardless though. You can never be too careful.