The association between surgical stress-related depression in bactericidal activities of neutrophils and the occurrence of postoperative infections was investigated. Bactericidal activities of neutrophils were measured in 19 patients undergoing esophagectomy, 15 gastrectomy, and 16 cholecystectomy. Five patients had complications of infection following esophagectomy. In 45 patients with no postoperative infections, intracellular killing index (KI) and superoxide anion production (SOP) levels decreased on postoperative day 1 while myeloperoxidase (MPO) activity increased on days 1–3. In 5 patients with esophageal cancer and postoperative infections, decreases in KI and SOP were less prominent, as compared to findings in 14 esophageal cancer patients without such problems but the MPO activity decreased on days 1–3. This evidence suggests that postoperative septic complications are not directly associated with surgical stress-related transient depression of bactericidal activities immediately after surgery but rather with neutrophil-mediated tissue injuries based on degranulation. © 1992 Wiley-Liss, Inc.