Little is known about neutrophil (PMN) apoptosis in the acute respiratory distress syndrome (ARDS). We used morphologic criteria to count apoptotic PMN in bronchoalveolar lavage fluid (BAL) of 35 patients on Days 1, 3, 7, 14, and 21 of ARDS and 13 patients on Days 1 and 3 of risk for ARDS. We found that the proportion of apoptotic PMN in BAL was low throughout the course of ARDS. There was no significant difference between the percentage of apoptotic PMN in patients at risk and patients with established ARDS or between patients who lived (2.4%) and patients who died (1.8%). When normal human PMN were incubated in ARDS BAL, a significantly lower proportion became apoptotic (50 ± 4%), as compared with PMN incubated in lavage fluid from normal volunteers (76 ± 7%, p < 0.05). This antiapoptotic effect of ARDS BAL was blocked by immunodepleting BAL of G-CSF and GM-CSF. We conclude that the proportion of apoptotic PMN recovered from the lungs of patients with ARDS is low throughout the course of ARDS. Furthermore, BAL from patients with ARDS prolongs survival of normal human PMN in vitro, and this effect is partially mediated by G-CSF and GM-CSF. Matute-Bello G, Liles WC, Radella F, II, Steinberg KP, Ruzinski JT, Jonas M, Chi EY, Hudson LD, Martin TR. Neutrophil apoptosis in the acute respiratory distress syndrome.