Platelet is blood's morphotic element in which intense energy metabolism takes place, which makes it possible to participate in the complex processes of the organism's homeostasis. The aim of the study was to analyse aerobic metabolism in the platelets, taking into consideration lipids peroxidation in patients with bladder cancer treated with the bacillus Calmette-Guerin (BCG) Mycobacterium suspension. The determination of superoxide dismutase (SOD-1) and malonyl dialdehyde (MDA) concentration activity constituted this evaluation's parameters. A group of 12 patients (4 women and 8 men) aged 54-67 years (average age 61) in which superficial bladder cancer was diagnosed were included in the study. Electroresection was carried out and subsequently, after 14 days, BCG Mycobacterium suspension was administered in intravesical instillations, in a 6-week cycle according to Morales. The material for the study was venous blood taken from the patients in three periods (before treatment, after the last clyster and 30 days after treatment) into the tubes with the addition of 1% EDTA in the ratio of 9 blood volumes to anticoagulant's one volume. Superoxide dismutase activity (Cu Zn--SOD) was determined according to Misra and Fridovich. The values were expressed in lamellar protein U/g protein. MDA concentration in platelet's TBARS was determined according to Pansa et al. MDA concentration included in TBARS was expressed in nmol/109 platelets. The controls were healthy volunteers in the same age range. In unaided studies a significant rise in superoxide dismutase (SOD-1) activity was obtained with the 1574.606 average before treatment > 2137.03 after treatment and 2646.4 after a month observation. Whereas MDA concentration increased in non-treated patients to 1.97, after treatment it dropped down significantly to 1.55 and sustained the downward trend after 30-day observation 1.4 nmol/109 platelets. The use of BCG intravesical clysters causes lipids peroxidation inhibition (decrease in MDA concentration) and the increase of SOD-1 activity results in smaller aggregation of platelets, preventing the formation of neoplastic metastases.