A double-blind study comparing the response of 21 patients with psoriatic arthritis to a series of three parenteral injections of methotrexate at 10-day intervals with the response to a similar series of three placebo injections has been reported. Methotrexate was found to be effective in suppressing the skin manifestations, decreasing joint tenderness and swelling, improving joint range of motion, and decreasing the erythrocyte sedimentation rate. Side effects included anorexia or nausea in 13 patients, burning sensation in the skin in ten, depression of the white blood cell count below 4,000/cu mm in seven, oral ulcerations in two, and mild hair loss in one. This therapy should be reserved for patients with severe disabling disease who have failed to respond to more conservative measures.