The content of beta-endorphin-like immunoreactivity (beta-EPLIR) in the anterior and neurointermediate lobe of the pituitary gland, the hypothalamus and the serum of the c57BL/6, BALB/C and DBA/2 inbred strains of mice was estimated at the resting state as well as 45 min after i.p. injection of either ethanol solution (3.0 g/kg.b.wt.) or saline. At the resting state, the neurointermediate lobe and the serum of the c57BL/6 mice showed the highest content of beta-EPLIR, while no statistically significant difference was noticed in the total beta-EPLIR content in the anterior lobe and hypothalamus. At 45 min post-ethanol treatment the beta-EPLIR content was increased in the serum of all three strains of mice studied and was decreased in the hypothalamus of the c57BL/6 mice only. Further analysis of the beta-endorphin peptides using sephadex G-75 chromatography and reverse phase high performance liquid chromatography indicated strain differences in the relative proportions of the various forms of beta-endorphin in the anterior lobe, neurointermediate lobe and the hypothalamus. These strain specific differences in the content and post-translational processing of beta-endorphin may be involved in some of the genetically determined differences in responses to ethanol by these inbred strains of mice.