Enteral nutrition with eicosapentaenoic acid (EPA; 20:5 n-3) and gamma-linolenic acid (GLA; 18:3 n-6) decreased pulmonary inflammation by reducing neutrophil counts and chemotactic factors in bronchoalveolar lavage fluid during acute respiratory distress syndrome (ARDS). We hypothesize that the anti-inflammatory effects of EPA and GLA may be due, in part, to induction of neutrophil apoptosis. The purpose of this study was to determine whether EPA and GLA, alone or in combination, trigger apoptotic cell death in the human promyelocytic leukemia HL-60 cell line. HL-60 cells were incubated with 10, 20, 50, and 100 micromol/L EPA, GLA, or various combinations of EPA and GLA for 2, 4, 8, 12, and 24 hs. Oleic acid (18:1 n-9) was used as a fatty acid control. Flow cytometry using dual staining with propidium iodide and annexin V-FITC assessed apoptosis, necrosis, and viability. Apoptosis was verified by DNA fragmentation as assessed by agarose gel electrophoresis. EPA, GLA, and various combinations of EPA and GLA significantly induced apoptosis and reduced cell viability in HL-60 cells. Viability was significantly reduced to the same extent with the combination of 50 micromol/L EPA\20 micromol/L GLA compared with 100 micromol/L EPA. These data indicate that EPA and GLA, alone or in combination, reduce cell survival by induction of apoptosis. Thus, induction of apoptosis by select dietary n-3 (EPA) and n-6 (GLA) polyunsaturated fatty acids may be the mechanism of the resolution of pulmonary inflammation in ARDS.