Two groups of rats were fed for 4 months either a lipotrope deficient (E-D) or a lipotrope supplemented (E-S) diet, both containing about 30% of total calories as ethanol (E). Two control groups consumed similar lipotrope deficient (S-D) and lipotrope supplemented (S-S) diets, but with sucrose (S) replacing ethanol. The rate of ethanol disappearance, microsomal protein content and total microsomal H2O2 generation were about 50% higher in the E-D group than in the other groups. Morphological studies revealed moderate to severe fatty changes only in the livers of the lipotrope deficient groups (E-D; S-D), while mitochondrial enlargement was observed only in the alcohol fed groups (E-S; E-D), particularly in the E-S group. State 3 respiratory rates with succinate and with malate-glutamate as substrates were about 50% reduced in the liver mitochondria of the animals of the E-S group, as compared with the other groups. From these results it is inferred that the lipotrope supplemented diet effectively prevented the alcoholic fatty liver but counteracted the alcohol-associated increases of ethanol oxidation rate, microsomal protein content and total microsomal H2O2 generation. On the other hand, the lipotrope supplemented diet was a necessary factor for the impairment of the mitochondrial respiratory function observed after chronic ethanol feeding.