Incubation of human neutrophils with the protein biosynthesis inhibitor cycloheximide for > or = 90 min results in a decreased ability to generate reactive oxidants during the respiratory burst. This implies that active protein biosynthesis is required to sustain the ability of these cells to generate reactive oxidants. However, short term incubation of neutrophils (40-60 min) with either cycloheximide or puromycin results in a significant increase in oxidase activity stimulated by either fMet-Leu-Phe (> 60%) or by leukotriene B4 (> 30%). However, after incubation for 40-60 min with these inhibitors of protein biosynthesis, the respiratory burst stimulated by PMA was unaffected whilst that stimulated by the particulate stimuli opsonised zymosan or latex beads was significantly inhibited. The enhanced oxidase activity stimulated by the soluble agonists was not explained by changes in receptor expression, alterations in intracellular Ca2+ levels or by enhanced degranulation. These results suggest that oxidase activity stimulated by soluble agonists in neutrophils is normally regulated by a short-lived, actively-synthesised protein(s).