Human neutrophils were isolated from healthy volunteers and exposed to either bicarbonate-containing (pH 7.4) or lactate-containing (pH 5.2) peritoneal dialysis solution in vitro. Superoxide production by neutrophils was measured by a method based on the superoxide dismutase-inhibitable reduction of ferricytochrome c. Bicarbonate-containing peritoneal dialysis solution was found to be superior to the lactate-containing one in facilitating the production of superoxide anion by human neutrophils.