What happens in the nose during an allergic reaction? Are there changes that a new drug could treat? What is the best way to test new drugs?The response of the nose to being exposed to cat allergen in someone who is allergic to cats. Symptoms, level of nasal blockage and cell and chemical changes that occur in the nose will be studied before and after being exposed to cat allergen. The investigators will also to see if giving repeated doses of allergen increases the response.Allergic rhinitis is a very common illness. There are over 500 million patients worldwide. It can increase the severity of associated asthma. Currently available drugs do not completely treat the symptoms. New treatments need to be found. A way of testing these drugs is very important. This study will investigate causes of the symptoms that occur in allergic rhinitis. It will also validate a proposed model to test new drugs. the Study Hypothesis is that a model of nasal allergen challenge shows an increased response (priming) with repeat challenges as determined by changes in nasal peak inspiratory flow.