OBJECTIVES:

I. Determine the efficacy of cysteine hydrochloride in preventing or decreasing photosensitivity in patients with erythropoietic protoporphyria.

PROTOCOL OUTLINE: This is a randomized, double blind, placebo controlled, crossover study.

Patients are randomly assigned to 1 of 2 groups to receive cysteine hydrochloride orally twice daily, 2 capsules with breakfast and 2 with lunch. Group 1 receives cysteine hydrochloride in drug ingestion period 1 followed by placebo in period 2. Group 2 receives placebo in period 1 followed by cysteine hydrochloride in period 2. Both groups ingest placebo for 1 week between the periods. Each drug ingestion period lasts 8 weeks.

Follow up phone calls are made at the end of months 1 and 3. All patients schedule follow up visits at the end of each drug ingestion period.

PROTOCOL ENTRY CRITERIA:

--Disease Characteristics-- Documented erythropoietic protoporphyria Determination of elevated protoporphyrin within the past year Experiencing photosensitivity --Prior/Concurrent Therapy-- No concurrent use of betacarotene --Patient Characteristics-- Other: Not pregnant or nursing Fertile female patients must use effective contraception while on study and for 3 weeks thereafter