IT has been shown previously that the addition of sorbitol to actively respiring suspensions of washed, motile ram spermatozoa causes an increase in the consumption of oxygen, accompanied by an oxidative conversion of sorbitol to fructose and followed by the aerobic glycolytic breakdown of fructose to lactic acid1. More recently, it was established that sorbitol, like fructose, actually occurs as a normal constituent in the seminal plasma of ram, bull, man and certain other species2. These findings make it highly probable that lactic acid, which accumulates in normal semen on aerobic incubation in vitro, is in fact in part the product of direct glycolysis from preformed seminal fructose, but partly also originates from the metabolism of sorbitol via fructose.