The aim of this study was to evaluate the usefulness of β-hexosaminidase for sobriety monitoring among alcoholics. In a group of 18 patients participating in fluvoxamine programme β -hexosaminidase activity in serum and urine was measured. It was found that: (1) β-hexosaminidase activity was elevated both in serum and in urine for one week and sometimes for two weeks after heavy drinking. It rapidly decreased as the patient continued abstinence. (2) The dynamics of decrease was bigger in urine. (3) Measurement of β-hexosaminidase activity in urine can be more useful than in serum because it is noninvasive and possibly gives less false positive results.