Nonsteroidal anti-inflammatory drugs (NSAIDs) produce their therapeutic activities through inhibition of cyclooxygenase (COX), the enzyme that makes prostaglandins (PGs). They share, to a greater or lesser degree, the same side effects, including gastric and renal toxicity. Recent research has shown that there are at least two COX isoenzymes. COX-1 is constitutive and makes PGs that protect the stomach and kidney from damage. COX-2 is induced by inflammatory stimuli, such as cytokines, and produces PGs that contribute to the pain and swelling of inflammation. Thus, selective COX-2 inhibitors should be anti-inflammatory without side effects on the kidney and stomach. Of course, selective COX-2 inhibitors may have other side effects and perhaps other therapeutic potential. For instance, COX-2 (and not COX-1) is thought to be involved in ovulation and in labor. In addition, the well-known protective action of aspirin on colon cancer may be through an action on COX-2, which is expressed in this disease. Moreover, NSAIDs delay the progress of Alzheimer's disease. Thus, selective COX-2 inhibitors may demonstrate new important therapeutic benefits as anticancer agents, as well as in preventing premature labor and perhaps even retarding the progression of Alzheimer's disease.