Interaction of ethanol and acetaldehyde with structures of rat liver cells nuclei was studied in vivo and in vitro using labelled compounds. After injection of 14C-ethanol and 14C-acetaldehyde into control and alcohol-consuming animals the radioactivity was found in carioplasm, non-histone proteins and residual DNA-protein complex. Relative value of specific radioactivity of all the chromatin components studied was practically similar after administration of either ethanol or acetaldehyde. The effect of such aldehyde dehydrogenase inhibitor as teturam led to a significant increase of the label incorporation into chromatin proteins. Acetaldehyde was shown to bind intensively with the isolated chromatin matrix. At the same time, radioactivity was not found in chromatin after incubation with labelled ethanol. The data obtained suggest that alterations in structure and functions of genetic cell apparatus under conditions of ethanol intoxication occurred mainly due to the action of acetaldehyde as a result of ethanol reduction.