The O consumption of frog nerve is depressed by Na iodoacetate even in high dilution, M/700 or beyond, the effect being progressive for at least 6 hrs. Addition of Na lactate markedly but not completely antagonizes the iodoacetate depression, both of respiration and of conduction as measured by action currents. Lactate alone may have some beneficial effect on the respiration of mammalian nerves, tending to lessen the spontaneous fall with time. In nerves with the sheath split, but not those with intact sheath, lactate also counteracts the breakdown of phos-phocreatin induced by iodoacetate. On stimulation in the presence of the halogen acid, phosphocreatin breakdown is no greater than in untreated nerve. The evidence favors the conclusion that nerve can burn lactic acid, although it remains doubtful that it does so normally or that this substance enters into the normal chemical sequence of activity.