A double-blind crossover study to compare 1200 mg. azapropazone per day with 100 mg. indomethacin per day was carried out on 34 patients with psoriatic arthritis and 16 patients with Reiter's disease. The same comparison was initiated in 8 additional patients but withdrawn in 3 cases because of side-effects to indomethacin, in 2 cases because of side-effects to azapropazone, and in the 3 remaining cases for other stated reasons. The results of the study showed no overall difference between the treatment results of azapropazone and indomethacin, but azapropazone seemed to be more effective in cases with psoriatic arthritis and indomethacin in cases with Reiter's disease. Indomethacin caused more side-effects than azapropazone. Neither drug seemed to influence the skin manifestations of either disease.