DURING anaerobic fructolysis by mammalian spermatozoa, fructose is reportedly metabolized by way of glycolysis to lactic acid1,2. Results from many anaerobic metabolic investigations in our laboratory, however, in which bovine spermatozoa were incubated for 4 h at 37° C have consistently yielded low lactic acid values in relation to the fructose utilized. This failure to account for all the metabolized fructose as lactic acid led us to investigate the possibility that other metabolic acids were being formed and, if so, to determine if the level of carbon dioxide in the gaseous phase, previously reported to influence spermatozoan metabolism3, affected the formation of these acids.