A clinical cooperative study involving 14 centers evaluated photochemotherapy (psoralen and high-intensity long-wave ultraviolet light [PUVA]) for psoriasis. Results from 465 patients treated with a PUVA-48 unit (equipped with 48 high-intensity UVA bulbs) and 110 patients treated with a PUVA-64 unit (equipped with 64 high-intensity UVA bulbs) confirmed the effectiveness of photochemotherapy for psoriasis. Clearing of psoriasis occurred in 85% of patients on PUVA-48 therapy. Mean number of treatments, joules per square centimeter, to clear, and total joules at clearing were similar to other reported trials. The plateau method of clearing resulted in lower joules per square centimeter at clearing, total joules per square centimeter, and number of treatments than the nonplateau method. Maintenance therapy groups were mainly M1 (once weekly) or M4 (no treatment for more than 60 days). No meaningful laboratory abnormalities were detected and ophthalmologic examinations showed a few abnormal results following PUVA. Short-term side effects were mainly erythema, nausea, and pruritus. The effectiveness and short-term safety of PUVA for psoriasis has now been confirmed by a second large cooperative study.