The aim of the current study is to replicate the COXA-0508-258 study in a multicenter, US setting, using a lower dose of ASA. It is expected that this study will not only confirm the results of the 258 study but show that the incidence of UGI ulcers on celecoxib is significantly less than on traditional NSAIDs and the incidence of UGI ulcers on celecoxib increases with the addition of ASA, but still is lower than traditional NSAIDs plus/minus ASA. This 7-day study is designed to compare the incidence of gastroduodenal ulcers associated with celecoxib 200 mg QD and low dose aspirin 81 mg QD and with naproxen 500 mg BID plus low dose aspirin 81 mg QD in healthy adults(50-75 years of age).