The generation from arachidonic acid and purification of large quantities of a series of monohydroxy-eicosatetraenoic acids (HETEs) which differed only in the position of the hydroxyl group permitted an in vitro analysis of the relative effects of the HETEs on a variety of human neutrophil functions. All of the HETEs elicited maximal neutrophil chemotactic responses of comparable magnitude, but the chemotactic potencies exhibited a distinct rank order with 5-HETE greater than 8-HETE:9-HETE (85:15, w:w) greater than 11-HETE=12-L-HETE. Peak chemotactic responses were achieved at concentrations of 1 microgram/ml for 5-HETE, 5 microgram/ml for 8-HETE:9-HETE and 10 microgram/ml for 11-HETE and 12-L-HETE. In the absence of a concentration gradient, the HETEs were similar in potency with respect to the stimulation of neutrophil chemokinesis and the enhancement of the expression of neutrophil C3b receptors. At optimally chemotactic and chemokinetic concentrations, none of the HETEs stimulated the generation of superoxide by neutrophils, altered the expression of neutrophil IgG-Fc receptors, or evoked the release of lysosomal enzymes. Methyl esterification of 5-HETE and 12-L-HETE reduced the chemotactic activity to less than 12% of that of the parent compound. The HETE methyl esters competitively inhibited the chemotactic activity of the homologous free acids by approximately 50% at equimolar concentrations, without inhibiting the chemotactic activity of formyl-methionyl peptides or of chemotactic fragments of the fifth component of complement (C5fr). The stimulus specificity of the competitive inhibition of chemotaxis by HETE methyl esters and the functional selectivity of the HETEs as compared to the formyl-methionyl peptides and C5fr, which stimulate neutrophil oxidative metabolism and lysosomal enzyme release, suggest that HETEs activate human neutrophils by a unique mechanism.