Serum samples collected from 45 untreated leprosy patients and 10 healthy subjects were studied for the activities of alkaline phosphatase, N-acetyl beta-glucosaminidase and beta-glucuronidase. A highly significant increase in the specific activity of these enzymes was observed in all types of leprosy patients as compared to controls. Increase in the level of circulatory hydrolytic enzymes could be a tissue damaging factor and may be responsible for many of the lesions seen in leprosy.