5-S-cysteinyldopa excretion after treatment with 8-methoxypsoralen and UVA light

The excretion of the specific melanocytic metabolite 5-S-cysteinyldopa was studied in patients with psoriasis treated by 8-methoxypsoralen and UVA light. A pronounced increase was found after only 2 days treatment, although no increase in pigmentation could yet be observed. Peak values for urinary 5-S-cysteinyldopa were noted after 1 or 2 weeks treatment. Increase in pigmentation persisted after the excretion maxima for 5-S-cysteinyldopa.