NSAIDs work by inhibiting the enzyme cyclo-oxygenase (COX), responsible for prostaglandin synthesis. This enzyme exists in two isoforms, COX-1 and COX-2. Inhibition of COX-1 is thought to be the main cause of the gastrointestinal unwanted effects of NSAIDs, whilst inhibition of COX-2 results in anti-inflammatory effects. [symbol: see text]Rofecoxib (Vioxx--MSD) and [symbol: see text]celecoxib (Celebrex--Searle) have been developed as selective inhibitors of COX-2. Rofecoxib is licensed for the symptomatic treatment of osteoarthritis, but not for rheumatoid arthritis. The manufacturer claims that "in clinical studies rofecoxib inhibits COX-2 but not COX-1", has "the power of high-dose NSAIDs--diclofenac and ibuprofen" and "superior GI safety profile compared to conventional NSAIDs". Celecoxib is licensed for symptom relief in osteoarthritis and rheumatoid arthritis. The manufacturer claims that celecoxib has "comparable efficacy and superior GI tolerability when compared to diclofenac or naproxen". Here, we review rofecoxib and celecoxib and consider whether they are safer than conventional NSAIDs.