The effect of norepinephine, an adrenomietic drug, and of pyrroxane, its antagonist, on diethylnitrosoamine (DENA) hepatocarcinogenesis was studied in albino rats. Norepinephrine was found to stimulate carcinogenesis, whereas pyrroxane--to inhibit this process; the latter drug decreased the incidence of multicentric tumours of the liver. In vitro experiments on the isolated rat atria showed low DENA concentrations (1x10(-6) to 1x10(-8) M) to sensitize the atrium adrenoreceptors to the endogenous and exogenous norepinephrine. A new hypothesis on the adrenergic component in the DENA carcinogenic effect caused by the endogenous norepinephrine is presented.