beta-N-acetylhexosaminidase exhibits a relatively high activity in human epididymis. Its isoenzymatic profile and immunological properties led us to conclude that the increased activity was not due to the expression of an isoform unrelated to the HEX A and B present in other human tissues. Measurement of enzyme levels in the three distinct epididymal regions revealed that in any given sample, activity was higher in the caput than in the corpus or cauda. Moreover, we found a striking correlation between beta-HEX activity in the caput region and concentrations of blood testosterone, suggesting a possible involvement of the hormone in modulating enzyme expression. Since the caput epididymis plays a role in the maturation of sperm cells, our data may be an indication that beta-HEX activity in the caput has a physiological relevance in human epididymis functions.