From 1987 to 1990, 719 subjects (385 males and 334 females) were screened, by means of urocystin-kit, for cystinuria and cystine lithiasis, in Epirus district (North-West Greece). The positive results were confirmed by chromatographic analysis of urine amino acids and laboratory tests. Forty patients, belonging to six cystinuric families, were identified. These patients were excreting 3.1 +/- 1.7 mmol/24 h of cystine in urine. All patients were treated by per os administration of alpha-MPG in daily doses of 400-1,200 mg/24 h). We therefore report the results of a 4 +/- 2 year follow-up of these patients. We conclude that treatment with alpha-MPG is very effective with minimal side effects in patients suffering from cystinuria or cystine urinary calculi.