The activites of six lysosomal acid hydrolases were measured in liver biopsy specimens from six patients with gargoylism and in post-mortem tissue from two patients. A marked diminution was noted for the activity of 4-methylumbelliferyl-βglactosidase in all patients with gargoylism. The deficiency of βgalactosidase did not seem to be due to the presence of an inhibitor in the liver. The activities of βglucuronidase, βacetylglucosaminidase, acid phosphatase and αfucosidase were significantly increased in some of the patients. The activity of αmannosidase was not significantly different from the values in the controls. © 1968 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.