This study was performed to analyze the relative and combined effects of ethanol and protein deficiency on bone histology and mineral metabolism in 4 groups of 7 animals each which were pair-fed during 8 weeks with 1) a nutritionally adequate diet; 2) a 36% (as energy) ethanol containing isocaloric diet; 3) a 2% protein, isocaloric diet; and 4) a 36% ethanol 2% protein isocaloric diet, respectively, following the Lieber-DeCarli model. Another group of five rats were fed ad libitum the control diet. The first and second lumbar vertebrae were removed after sacrifice, and processed for histomorphometrical analysis of undecalcified bone samples. Blood and 24-h urine were also collected. Protein malnutrition, but not ethanol, leads to osteoporosis and reduced osteoid synthesis, whereas ethanol and protein malnutrition both lead to impaired bone mineral apposition and increased urinary hydroxyproline excretion. These changes are accompanied by an increase in serum parathormone and serum 1,25 dihydroxy vitamin D3, a slight hypomagnesemia, hypercalciuria and hyperphosphaturia; protein deficiency plays an independent role in these alterations, whereas both ethanol and protein deficiency exert independent effects on decreasing serum testosterone levels; this last alteration may contribute to the bone changes mentioned before.