Serum beta-glucuronidase activity was estimated using phenolphthalein mono-beta-glucuronic acid as substrate in 176 individuals including 72 lepromatous leprosy patients, 24 patients of borderline leprosy, 42 of borderline tuberculoid and 38 healthy controls. Of these, 35 patients (20 with lepromatous leprosy, 5 with borderline leprosy and 10 with borderline tuberculoid) were untreated. The enzyme levels were increased significantly in all types of leprosy, the highest levels being seen in treated lepromatous leprosy patients (105.0 SU). There was also a significant difference in the enzyme activity between untreated patients and those on combined dapsone and rifampicin therapy, in all three types of leprosy. Among untreated patients, the maximum value observed in lepromatous leprosy was 93.4 SU. The lowest enzyme level in healthy control was 19.5 SU and the maximum was 54.0 SU. The results suggest that in leprosy patients, especially in those on daily multidrug regimens, there is an extensive damage of leucocytes and liver cells where the enzyme is largely present.