This double-blind randomised study investigated the role of sulphydryl-containing agents in the management of recurrent attacks of ulcerative colitis. To this end, DL-cysteine (200 mg 4 times daily) and DL-methionine-methyl sulphonium chloride (MMSC, 500 mg 4 times daily) were administered orally. Patients with recurrent attacks of moderate proctosigmoidal ulcerative colitis, despite prophylaxis by oral sulphasalazine (2 g daily), were given prednisolone by mouth, 10 mg four times a day, sulphasalazine by mouth, 500 mg four times a day, and morning and evening retention enema (Predsol 20 mg) alone or with cysteine or MMSC. After 2 weeks of treatment with sulphasalazine and prednisolone, 51% of patients (n = 45) were symptom free. Addition of cysteine (n = 46) or MMSC (n = 47) to this regimen controlled the symptoms within 2 weeks in 85% of patients (p