This is a record of the concentrations of the nonenzyme components of the Embden-Meyerhof system in mouse brain measured at brief intervals after the production of complete ischemia by decapitation. All of the 18 recognized active components were looked for. Of these, 1,3-diphosphoglycerate did not reach levels measurable by the procedures used. Additional substances determined were glycogen, phosphocreatine, creatine, adenosine 5’-phosphate, cu-glycerophosphate, and triphosphopyridinenucleotide and its reduced form. The pyridine nucleotide values are only provisional. Considerable attention is devoted to methodology, since there are numerous possibilities for serious errors in preparation of samples as well as in the analyses for individual substrates. The substances measured account for all the known significant sources of energy available to the brain after its blood supply is cut off. Therefore it is possible to calculate the metabolic rate during the brief period of survival, as well as the time sequence according to which the brain taps its reserve sources of energy. Ischemia resulted in increases in glycolytic rates of at least 4to 7-fold in different experimental groups of mice. The coincident changes in substrate concentrations show which steps were facilitated to make this increase in flux take place, i.e. which steps control glycolysis in brain. These steps are the phosphorylations of glucose and fructose 6-phosphate, and the phosphorolysis of glycogen. There is no evidence that facilitation occurs at any other step in the glycolytic pathway.