Laparoscopic cholecystectomy has a better postoperative outcome than the traditional open technique, which has been shown to significantly affect respiratory muscle function. The aim of this study was to investigate the effects of laparoscopic surgery on respiratory function, and particularly that of the respiratory muscles. Respiratory muscle strength was assessed in 26 patients who underwent laparoscopic cholecystectomy and in 25 who underwent open cholecystectomy by measuring mouth pressure during maximum static inspiratory (PImax) and expiratory (PEmax) efforts. PImax, PEmax, and blood gases were measured 24 h preoperatively (-24 h) as well as 24 h (+24 h) and 48 h (+48 h) postoperatively. FEV1 and FVC were measured at -24 h and +48 hr, and the ratio of FEV1 to FVC (FEV1/FVC) was calculated. PImax decreased at +24 h and +48 h in both groups, but this decrease was significantly greater in the patients who had open surgery, (p < 0.01, and p < 0.005, respectively). Similarly, PEmax was significantly smaller in the open- than in the laparoscopic-surgery group (p < 0.0001) at +48 h. Spirometric indices showed a more severe restrictive defect at +48 h after open surgery than after laparoscopy (p = 0.01). The arterial oxygen tension (PaO2) was significantly greater in the laparoscopic- than in the open-surgery group at +24 h (p < 0.007). Laparoscopic cholecystectomy caused smaller decreases in respiratory muscle strength than did open surgery. This accords with the hypothesis of phrenic nerve inhibition during open surgery. The results are of clinical importance, since they may explain the different outcomes with the two techniques.