Understanding the regulatory and metabolic functions of the HOG (High Osmolarity Glycerol) genes in the yeast Saccharomyces cerevisiae may provide the means to enhance both ethanol production and the ethanol/glycerol ratio in industrial fermentations. High resolution C-13-NMR was used to study the formation of metabolites fr om [1-C-13]-labeled glucose by wild-type and hog1, hog2, and hog1 hog2 mutants under controlled conditions and increased osmolarity with 400 mM NaCl. Time-course spectroscopy of anaerobic suspensions showed[2-C-13]ethanol and the osmolyte [1,3-C-13]glycerol as the major end products of glycolysis under control and saline conditions. Glycerol and ethanol production increased in all strains after the shift to high-salinity medium; however the rates and yields for glycerol in all mutants were lower than in the wild type. The hog2 mutant showed a smaller decrease in glycerol yields and production rates than the hog1 mutant, and the hog1 hog2 strain showed a quantitatively additive reduction, suggesting that the hog1 and hog2 mutants respond to high salinity by two independent mechanisms. Enhancement of the ratio of ethanol/glycerol production rates was achieved in the hog mutants under control and high salinity conditions.