Papaverine - (3,4-dimethoxybenzyl)-6,7-dimethoxyisoquinoline, PAP) is a member of the benzylisoquinone subgroup of the opium alkaloids. It has been widely used for treating such diseases as pulmonary arterial embolism or renal and biliary colic. The aim of the research was to evaluate the influence of papaverine and melatonin on GSH metabolism in blood, brain, liver and kidney of mice. The distinct decrease in the GSH concentration was found after injection of papaverine. This decrease was reversed by earlier injection of melatonin. The obtained results suggest that the inhibiting effect of papaverine on the GSH level is connected with disturbances in energy mechanisms in cells, mainly inhibition of aerobic energy metabolism.