Arachidonate stimulates the production of large quantities of superoxide by human neutrophils: 93.8 +/- 12.5 S.D. nmol of O2(-)/min/10(7) cells. This rate is comparable to that observed with the most effective neutrophil-stimulating agents previously reported. Other cis-unsaturated fatty acids are also capable of eliciting this response, the order of effectiveness being: arachidonate greater than gamma-linolenate greater than linoleate greater than oleate. Linolelaidate, myristate, and palmitate are ineffective. These data are discussed in relation to recent reports concerning the oxidation of arachidonic acid by human neutrophils and by a cell-free system that generates superoxide and hydrogen peroxide.