The effects of omeprazole on polymorphonuclear neutrophil (PMN) chemotaxis, superoxide generation, degranulation and translocation of cytochrome b-245 were investigated. Omeprazole (10(-6) - 5 x 10(-3) mol/l) reduced chemotaxis under agarose in a dose dependent manner, and the effect was irreversible. Superoxide anion generation was inhibited 50% at a concentration of 2.5 x 10(-5) mol/l and completely abolished at 5 x 10(-3) mol/l. Acid degraded omeprazole also inhibited O2- generation. Omeprazole did not scavenge O2- generated in a cell free xanthin-xanthine oxidase system. Degranulation by PMNs was inhibited only by omeprazole in concentrations above 10(-4) mol/l. Translocation of cytochrome b-245, essential for generation of O2-, was not affected by omeprazole. In conclusion, the anti-ulcer agent omeprazole in concentrations obtained during intravenous administration may inhibit the function of PMNs in vitro.