The ability of polymorphonuclear leukocytes, monocytes and peritoneal macrophages to mount a respiratory burst in continuous ambulatory peritoneal dialysis (CAPD) fluids was tested in a phorbol-myristate acetate stimulated chemiluminescence assay. Fresh CAPD fluids depressed the chemiluminescence response of all three types of phagocytes tested to less than 18% of their chemiluminescence response in control buffer. When tested in spent CAPD fluids the suppression of chemiluminescence was 30-32%. Oxygen consumption of polymorphonuclear leukocytes was depressed in fresh CAPD fluids to below 40%. Both phagocytosis of Escherichia coli by and bactericidal capacity of polymorphonuclear leukocytes and monocytes were suppressed in fresh CAPD fluids but not in spent effluents. The influence of acidic pH and hyperosmolality on phagocytic functions were studied separately by modifying the acidity or the glucose content of the control buffer. pH values below 6.0 significantly inhibited chemiluminescence but not phagocytosis. Under hypertonic conditions, both phagocytosis and chemiluminescence were inhibited. We conclude that the currently available CAPD solutions are beyond the limits of acid and osmotic tolerance of human phagocytic cells, and may thus compromise the peritoneal defenses of CAPD patients.