Photochemotherapy, a recently developed method of treatment, is based on the effect of light on a systemically administered photo-active substance. 152 patients with severe generalized psoriasis were exposed, after oral administration of 8-methoxy-psoralen, to a high-intensity UVA light source radiating at a continuous spectrum between 320 and 390 nm (maximum at 365 nm). Radiation doses ranged from 1.4 to 4.8 J/cm2 and were progressively increased. Complete remission occurred in 141 patients, satisfactory improvement in the remaining 11. It required 12+/-6 radiation sessions (-/x +/- s) to obtain remission, mean duration of treatment being 22 +/- 14 days. Apart from a neutral ointment no other local or systemic therapy was used. Photochemotherapy completely healed the psoriatic foci leaving evenly tanned, cosmetically appealing skin. All patients were treated at intervals as out-patients (average once a week or ev-ry other week), and remained without recurrence for up to 400 days. No local treatment is required with photochemotherapy, which is very effective, simple, harmless and does not stress patient or doctor. Interval treatment maintained the cure.