In a double-blind trial 40 patients with ostheoarthritis were treated for relief of pain with ketoprofen or with the N-methyl-d-glucamine salt of indomethacin, both drugs being administered i.m. at the dosage of 100 mg/day for 12 days. Ketroprofen and the indomethacin salt significantly improved pain, functional capacity and walking distance, while only the former reduced the knee size in the patients with gonarthritis. The two drugs showed roughly the same latency period and the same duration of activity. Ketoprofen was perfectly tolerated: on the contrary, in one patient treated with the indomethacin salt, the treatment was stopped because of vascular hypotension and cutaneous rash. A significant increase of blood urea nitrogen was observed only in the group of patients treated with the indomethacin salt.