The influence of cytotoxic agents adriamycine (AD) and ethydium bromide (EB) on Ca(2+)-dependent K+ channels of erythrocytes was investigated. The incubation of erythrocytes with agliconic part of AD (without aminosugar residue) increased Ca(2+)-dependent K+ efflux induced by low concentration of propranolol, while EB suppressed the activating effect of propranolol. EB, verapamil and triphluoroperazine inhibited Ca(2+)-dependent K+ efflux induced by high doses of propranolol. The incubation of erythrocytes with AD took off the inhibitory action of EB and verapamil but did not influence the blocking effect of triphluoroperazine. Both AD and EB did not influence Ca(2+)-dependent K+ channels induced by Ca(2+)-ionophore A23187, and Pb(2+)-dependent K+ efflux from erythrocytes. It is suggested that opposite effects of AD and EB on Ca(2+)-dependent K+ channels are due to activation by AD and inhibition by EB of system of Ca2+ transport into cells, but not on their action directly on K+ channel.