Our results on the action of mitomycin C in the treatment of urethral stricture indicate an additional effect on the regulatory system of the cell, in particular, disruption of the arginase / NO-synthase system of blood lymphocytes, leading to an imbalance of lymphocyte regulatory systems and NO regulatory function. Decreased H 2O2-induced iNOS activity by mitomycin C suggests that these antibiotics may prevent NO overproduction in blood lymphocytes. Nitric oxide, which is produced in excess in pathological conditions of the body, has a pronounced cytotoxic effect due to the formation of peroxynitrite – a product of the interaction of NO and superoxidanion-radical, capable of destroying almost all components of the cell. It is likely that one of the mechanisms of action of mitomycin C is a decrease in hyperproduction of NO.