[en] Diethone (2,6-Dimethul-3,5-dietoxycarbonyl-1,4-dihydropyridine) is an anti-oxidant, the metabolism and pharmacokinetic properties of which have been already investigated in rats and rabbits. Experimental data on its absorption, distribution and excretion from rats are also available. The favourable effects of this drug for the prevention and treatment of radiation injuries of skin could be observed in animal experiments. The aim of the present work was to follow the Diethone-related changes of some parameters of 'normal' and malignant cell cultures of human origin as well as the studies of direct effect of Diethone on the functional condition of immune competent cells, i.e. human leukocytes. The parameters examined in our experiments have reflected the proliferation activity of the cells, he ligand-binding capability of their plasma membranes, the cytolytic activity of leukocytes (effector cells) against tumor cells (targets). The examined cellular biological parameters were as follows: mitotic index, labeling index, lectin (Concanavalin A, Con A) binding and natural cytotoxicity of incubation medium of human leukocytes. The effects of various concentrations (10, 50, 100 μg/ml) of Diethone were tested