Previously published work has indicated that polyunsaturated fatty acids (PUFA) may enhance neutrophil-mediated damage to host tissues. We have found that endothelial detachment was significantly increased by neutrophils pretreated with docosahexaenoic (22:6, n-3) and arachidonic (20:4, n-6) acids at 10-40 microM but not by eicosapentaenoic acid (20:5, n-3). Endothelial cell lysis as measured by 51Cr release was unaffected. The extent of detachment was dependent on both fatty acid and neutrophil pretreatment concentrations. A specific leukocyte elastase inhibitor abrogated the increased detachment but catalase had no effect. Measurement of prostaglandin I2 synthesis as an alternative nonlytic assay of endothelial function indicated that 20:4 but not 20:5 was able to stimulate neutrophil-induced endothelial PGI2 synthesis. Although all three PUFA (3-33 microM) were found to stimulate release from neutrophil-specific granules, only 22:6 and 20:4 could stimulate release of the azurophilic granules containing elastase to any significant extent. Saturated fatty acids (20:0 and 22:0) and the methyl ester of 22:6 did not cause either neutrophil-mediated endothelial detachment or degranulation. We conclude that neutrophils pretreated with 22:6 or 20:4 but not 20:5 can decrease endothelial integrity through detachment involving neutrophil elastase. These findings may have important implications for the dietary use of fish oils rich in n-3 fatty acids.