Transient immunosuppression in patients during anesthesia and surgery may cause postoperative infections. In the immunity against pathogens the processes of non-specific defence are of special importance and engage neutrophils as the major cell type. The aim of this study was to monitor activity of neutrophils during and after surgery, applying different methods of anesthesia. The status of neutrophils was determined by evaluation of chemotactic, phagocytic and chemiluminescence (bactericidal) activities. The study included 78 patients, who underwent surgery due to pathological injury-effected changes or due to varicose veins of extremities. Blood samples for determination of the neutrophil activity were taken just before anesthesia, when the symptoms of anesthesia occurred, 15 min after starting of surgery, 24 h and 5-7 day after surgery. In majority of patients we observed neutrophilic leukocytosis. There was a statistically significant correlation between leukocytosis and percentage of neutrophils in the subsequent days after surgery, depending on a kind and extension of surgical intervention. In addition, we have found a decrease in chemotactic, phagocytic and bactericidal activity after all kinds of anesthesia. The decrease in the phagocytic activity lasted longer, usually at least 24 h after surgery, whereas chemotaxis and chemiluminescence returned quickly to control levels. In the spinal anesthesia the chemiluminescence was not altered; this phenomenon could result from blockade of the sympathetic nerve system and activation of neutrophils metabolism. The brachial plexus blockade had the statistically smallest effect on the function of neutrophils. In the long-term anesthesia (longer than 2 h), particularly using halothane, we have observed depressed values of chemotaxis, phagocytosis and chemiluminescence which lasted longer than in other studied group of patients. We conclude that monitoring of the neutrophil functions is a useful form of studying immune reactions of patients to anesthesia and surgery.