It is now established that prostanoids play important roles in many cellular responses and pathophysiologic processes including modulation of the inflammatory reaction, erosion of cartilage and juxtaarticular bone, gastrointestinal cytoprotection and ulceration, angiogenesis and cancer, hemostasis and thrombosis, renal hemodynamics, and progression of kidney disease. The initial step in the formation of prostanoids, i.e., the conversion of free arachidonic acid (AA) to prostaglandin (PG)G(2) and then to PGH(2), is controlled by two PGH synthases (COX-1 and COX-2). Selective inhibitors of COX-2 (coxibs) have established efficacy in the treatment of pain and inflammation comparable to that of nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) but exhibit enhanced gastrointestinal safety. Several lines of evidence suggest a critical role of COX-2 expression in cancer and selective COX-2 inhibitors may represent novel chemopreventive tools. Moreover, it has been suggested that COX-2 inhibitors may contribute to maintain high levels of chemotherapeutics in tumor tissues by preventing the overexpression of the multidrug resistance protein MDR1/P-gp. The place of COX-2 inhibitors in neurological diseases continues to attract basic and clinical investigation. The possible involvement of COX-2 in neurodegeneration, substained by the results of epidemiological studies with nonselective NSAIDs, has not been confirmed by the results of initial clinical trials with coxibs in Alzheimer's disease. Recently, the involvement of COX-2 in endogenous cannabinoid system has been suggested. Interestingly, COX-2-mediated oxygenation of arachidonylethanolamide (anandamide, AEA) and 2-arachidonylglycerol (2-AG) provides diverse sets of novel lipids that are structurally related to prostaglandins.