The efficacy and side-effect profiles of two formulations of indomethacin were compared in a multi-centre, double-blind, crossover study in 77 patients with osteoarthritis. Patients were allocated at random to receive 75 mg indomethacin per day either as 1 controlled-release tablet at night or as 1 immediate-release capsule given 3-times daily for a period of 4 weeks, after which patients were crossed over to receive the alternative treatment for a further 4 weeks. Pain scores, daily symptomatology and the requirement for escape analgesia recorded by the investigator and patient indicate that controlled-release indomethacin tablets, 75 mg given at night, were as efficacious as immediate-release indomethacin capsules, 25 mg given 3-times daily, in the treatment of osteoarthritis. The side-effect profiles of the two formulations were similar.