In this study we have investigated the influence of sodium hypochlorite (SH) on the blood leukocytes in rats (experimental part) and the possible applications of SH in patients with acute pyelonephritis. Experimental part was performed on 35 white inbreed male rats. Clinical part included 2 groups of patients from urological clinic. First group included 20 patients with acute pyelonephritis (AP). Leucocyte’s amount in blood before and at 1-3 and 7-10 days aer SH injection and indirect electrochemical blood oxidation (IEBO) was monitored. The second group contained 5 patients in which an AP was diagnosed aer operation, and the subpopulation of leukocytes were studied aer single IEBO session. The parameters were monitored before IEBO and at 1-3, 3-4 and 7-10 days aer. Experimental and clinical investigations showed that SH had a short, controlled, dosedependent immunosuppressive action directed at monocytes, lymphocytes and neutrophils. SH can limit the power of cell and humoral defence of the body in situations with massive bacterial load in patients with AP and clinical signs of systemic inflammatory response syndrome. SH activates immune system aer single injection at 3-4 and 7-10 days, which is evident as the rise in the all leukocyte subpopulations by means of 5-21% and as the increase of proliferative activity of lymphocytes by 28% and significant increase of effector function of activated T-lymphocytes 1.72 times.