Objectives: To investigate the activity and biochemical properties of glycosidases in the peritoneal fluid of infertile patients with or without endometriosis in comparison with fertile women. Design and methods: Peritoneal fluid was collected from 29 women undergoing a laparoscopy. The sample was separated into the following groups: fertile women (n = 11), infertile with endometriosis (n = 11), and infertile without endometriosis (n = 7). The activity of glycosidases was determined with specific p-nitrophenylglycosides as colorimetric substrates. Results: The activity of alpha-fucosidase, alpha-glucosidase, alpha-mannosidase, beta-galactosidase, beta-glucuronidase, and beta-N-acetylhexosaminidase was investigated. Enzymatic activities of alpha-fucosidase and beta-N-acetylglucosaminidase were detected in higher amounts than other glycosidases. The activities of alpha-iucosidase and N-acetylglucosaminidase were increased in the case of infertile patients without endometriosis, while beta-galactosidase was increased in endometriosis patients. Enzyme properties as pH optimum, pH stability, thermal stability and inhibition by specific carbohydrates were similar for both control and infertile samples. Analysis of kinetic parameters indicate that V-max values of glycosidases were higher for infertile samples than their respective controls. Conclusions: The results indicate that higher amounts of glycosidases are present in the peritoneal fluid from infertile patients. The elevated activity of these hydrolytic enzymes suggest possible deleterious effect on gametes, and could explain some cases of infertility. Copyright (C) 1998 The Canadian Society of Clinical Chemists.