This paper aims to assess the relationship between the urinary activity of N-acetyl-ß-D-glucosaminidase (NAG) and its isoenzyme B (NAG-B) and cadmium (Cd) concentration in the urine as well as to evaluate which of these lysosomal enzymes may be a more useful biomarker for the monitoring of Cd-induced tubular damage. For this purpose we have used an experimental model in rats chronically exposed to Cd in which we noted damage to the proximal tubules, including lysosomes. In rats intoxicated with 5 mg Cd/dm3, the urinary activities of NAG and NAG-B increased after 12 weeks of treatment, while at 50 mg Cd/dm3 - activities increased already after the 1st week. The urinary Cd excretion in Cd-exposed rats, st week. The urinary Cd excretion in Cd-exposed rats, but not in the non-exposed ones, positively correlated with the activities of NAG and NAG-B. A positive correlation which was observed between NAG and NAG-B activities was stronger in Cd-exposed animals than in those not exposed. The results of the present and our previous histopathological and histoenzymatic studies, confirm the usefulness of total NAG and NAG-B as sensitive markers of proximal tubular injury for the monitoring of chronic exposure to Cd. Taking into account the strong correlation between the total NAG and its isoenzyme B, similar correlation coefficients between their activities and Cd concentration in urine and simplicity of total NAG determination compared to that of NAG-B, one can conclude that the determination of total NAG is suitable for the monitoring of exposure to Cd. As the urinary activity of total NAG is a sum of activities of several isoenzymes, which may be influenced by various factors, and the intralysosomal localization of NAG-B, we hypothesize that NAG-B should be recommended as a sensitive and useful marker for routine monitoring of chronic exposure to Cd.