The effects of prolonged ethanol administration (10% ethanol-water solution as the sole drinking fluid for 6 to 14 weeks) on brain ribosomes and tRNA were studied in Sprague-Dawley rats. For comparison, liver ribosomes were also studied. The amounts of ribosomes in brain and liver and the proportion of the ribosomes in the form of polyribosomes were found to be essentially unaltered after 14 weeks of ethanol intake. In the brains of ethanol-treated animals, the total amount of unfractionated tRNA was slightly increased after 6 weeks. The acceptance of radioactive glutamic acid, leucine, methionine, phenylalanine, proline and serine by tRNA was also unaltered. When the activities of aminoacyl-tRNA synthetases specific for the six amino acids were studied in cross-over experiments, no changes were found. Comparison of the isoaccepting species of [14C]Met-, [14C]Leu- and [14C]Ser-tRNA by chromatography on benzoylated DEAE-cellulose revealed significant alteration in the chromatographic profile of [14C]Leu-tRNA derived from the brains of the alcohol-treated rats. These results suggest that prolonged intake of relatively small amounts of ethanol is accompanied in rats by essentially no alterations in total amounts of brain and liver ribosomes, brain tRNA, or activities of several aminoacyl-tRNA synthetases. As demonstrated by the leucine tRNAs, however, the quantitative distribution of isoaccepting tRNA species may change.