The production of chlorinated oxidants such as hypochlorous acid is a central antimicrobial and immunoregulatory function of neutrophils. Neutrophil hypochlorous acid production was compared in patients undergoing uncomplicated laparoscopic surgery (group 1) and those submitted to conventional open surgery (group 2). Preoperative peak hypochlorous acid production was similar in the two groups (mean(s.e.m.) 0.60(0.05) versus 0.69(0.06) nmol/min respectively). In group 2, mean(s.e.m.) neutrophil hypochlorous acid production fell significantly on day 1 after surgery (0.36(0.05) nmol/min; P < 0.01) but this did not occur in group 1 (0.63(0.07) nmol/min). By day 6 hypochlorous acid kinetics had returned to preoperative levels in both groups. Minimally invasive surgery is less disruptive of neutrophil function than conventional open procedures.