The aim of the present study is to analyse the relative and combined effect of ethanol and protein malnutrition on muscle changes in ethanol-fed rats. The study was performed in 32 animals divided into four groups, fed with the Lieber-DeCarli control, 36% ethanol, 2% protein, and 36% ethanol/2% protein-containing diets, respectively. Right gastrocnemius muscle was removed two months later, and histochemical-morphometrically studied. Type IIb fibre atrophy was observed both in the alcoholic and protein-deficient animals. The combination of these factors led to a slightly more marked atrophy. Malnutrition led to a decrease in type I fibre diameter; ethanol caused an increase in their size; whereas concurrent administration of ethanol and a protein deficient diet led to type I fibre atrophy. The proportion of type IIb fibre decreased in the three experimental groups with respect to the control group, especially in the alcoholic, protein-deficient animals. Thus, malnutrition potentiates the effect of ethanol except for changes in type I fibre diameter, in which the effects are opposite.