Article abstract Two labeled steroid conjugates, 114C]-dehydroepiandrosterone-3-beta-N-acetylglucosaminide and ['4C]-testosterone-17-beta-N-acetylgluco-saminide, were used to assay the steroid-hexosaminide cleaving activity of liver preparations from patients with Tay-Sachs disease, Sandhoff-Jatzkewitz disease, and the AB variant. The results were compared with those obtained with normal controls. The steroid hexosaminidase activity was directly proportional to the artificial substrate cleaving activity (4-methylumbelliferyl-beta-D-N-acetylglucosaminide) in both the A and B components of beta-N-acetylhexosaminidase. The constant ratio of specific enzymatic activities towards the three substrates in each case examined suggests that the same enzymes are active toward all three substrates. In spite of the decreased steroid hexosaminidase activity in Sandhoff-Jatzkewitz disease, no increased excretion of steroid hexo-saminides was observed in the urine of patients with this disease.