"Open" surgical procedures are followed by profound changes in endocrine metabolic function and various host defense mechanisms, impaired pulmonary function, and hypoxemia. These physiologic changes are supposed to be involved in the pathogenesis of postoperative morbidity. Endoscopic surgery, mostly studied during laparoscopy, when compared with similar open operations, has no important effects on classic endocrine metabolic responses but may slightly reduce inflammatory responses and various immune functions, although the data are not consistent. In contrast, most data show improvement of postoperative pulmonary function and less hypoxemia with endoscopic operation. The slight modification of surgical stress responses by endoscopic surgery is in contrast to the common, though not universal, demonstration of less pain, shorter hospital stay, and less morbidity after endoscopic surgery. In conclusion, endoscopic surgery has so far not been demonstrated to have important modifying effects on classic endocrine metabolic responses and only a slight inhibitory effect on various inflammatory responses, but with improved pulmonary function and less hypoxemia. More data are needed from major operations where differences are more likely to be found. The clinical consequences of these findings in relation to all over surgical outcome remain to be defined, but effective pain treatment, stress reduction by other techniques, and provision of an active rehabilitation program with early mobilization and oral feeding may be more important than the choice between an endoscopic technique versus "open" operation per se to improve outcome.