Because a patient with arthritis (especially rheumatoid arthritis) may respond to one NSAID but not another, any addition to the ranks of these agents may be of clinical benefit to at least some of the millions of patients afflicted with rheumatoid arthritis, osteoarthritis and related conditions. In terms of potency both as an antiinflammatory and as an analgesic, carprofen appears to be in the middle of the NSAID range--roughly one-fourth as potent as indomethacin, and five times as potent as ibuprofen, milligram for milligram. The two most obvious potential advantages of carprofen are that it seems to have a low profile of major gastrointestinal adverse reactions (it may cause minor complaints similar to those seen with indomethacin, but thus far has caused no documented gastric or duodenal ulcers at 300 mg/d); and that, like naproxen, it offers the convenience of twice-a-day dosing. In clinical experience thus far, the two most bothersome adverse effects seen with carprofen have been a rare but serious photosensitivity reaction and minor, temporary elevations of liver function tests in approximately 14-20% of patients treated (although as yet there have been no reported cases of jaundice or hepatitis). For some patients with rheumatoid arthritis, osteoarthritis or related conditions, particularly for those who cannot tolerate aspirin or indomethacin or who want or need the convenience of twice-a-day dosing, carprofen may represent a useful therapeutic option to the NSAIDs previously available in this country.