Animal and human data demonstrate that cyclooxygenase (COX)-2 upregulation in osteoarthritis and rheumatoid arthritis is associated with the pain and inflammation of the disease state. The COX-1 isoform, however, is a constitutive enzyme with homeostatic functions. Unlike conventional nonsteroidal anti-inflammatory drugs, which inhibit both forms of the COX enzyme, celecoxib inhibits COX-2 preferentially to COX-1 in vitro. Celecoxib reversed signs of arthritis and pain in an animal model as effectively as indomethacin. Data from murine studies as well as in vitro and epidemiologic data indicate that COX-2 plays a role in the development of colon cancer, and epidemiologic studies also suggest that COX inhibition can slow the progression of Alzheimer's disease.