A randomized double-blind within-patient study of mefenamic acid compared with ibuprofen was performed on forty patients with rheumatoid arthritis. It was concluded that mefenamic acid and ibuprofen had an analgesic and anti-inflammatory effect which was not significantly different in the dosages employed. Apart from six complaints of drowsiness of ibuprofen with two complaints on mefenamic acid, the side-effects were similar.