We studied the in vitro effects of peritoneal dialysis fluids (PDF) containing 1 and 1.5% amino acids (AA) as compared to approximately equiosmolar glucose (GLU)-based PDF (1.5 and 4.25%) and control buffer, respectively, on peritoneal macrophage (PMØ) function. The media were tested at original pH (5.3-5.5) and after pH adjustment to 7.4. PMØ were isolated from the effluents of 10 on continuous ambulatory peritoneal dialysis (CAPD) patients and tested for luminol- and lucigenin-enhanced chemiluminescence (CL), superoxide generation measured by cytochrome c reduction, killing capacity and phagocytosis after incubation (30 min, 37°C) in the PDF used. All AA-based PDF exhibited a statistically significant depressive effect on integral CL response, O-2 production and bacterial killing of PMØ at pH 7.4 in comparison with pH-adjusted GLU-based PDF of similar osmolality and buffer. Exposure of PMØ to acidic AA-based media did not result in a significantly different suppression of the oxidative metabolism and the killing capacity as compared to fresh GLU-based fluids. Phagocytosis of PMØ did not show significant differences after incubation in the solutions studied. Thus, the AA-based PDF employed compromise the oxidative metabolism and the killing capacity of PMØ at pH 7.4 in vitro significantly more than GLU-based fluids. Since pH-identical and almost equiosmolar PDF were compared, the specific composition of the AA-based fluids, especially the high content of lactate and several essential AA, could be responsible for this detrimental