This study will determine whether glucosamine, chondroitin sulfate and/or the combination of glucosamine and chondroitin sulfate are more effective than placebo and whether the combination is more effective than glucosamine or chondroitin sulfate alone in the treatment of knee pain associated with osteoarthritis (OA) of the knee after six months of follow-up. These substances, marketed in the United States as dietary supplements, have been widely touted by the lay press and by anecdotal personal experience as effective in treating OA. To date, however, only a few small studies have been published in the worldwide literature. The study proposed herein has been carefully constructed to definitively determine the efficacy of these agents.