Acid phoshatase (AcP), beta-glucuronidase (GR) and N-acetyl-beta-D-glucosaminidase (NAG) activity in neutrophils obtained from the peritoneal fluid of 50 patients with terminal renal failure treated by intermittent peritoneal dialysis, and of 30 control subjects with normal renal function was semiquantitatively scored using a cytochemical method. This study was repeated in 22 dialyzed patients during the course of bacterial peritonitis. A significant decrease in the AcP score and an increase in the GR score were found in the neutrophils from dialyzed patients. In dialyzed patients with peritonitis, the GR and NAG scores were higher that in those without this complication.