The source of energy for life is the tissue mitochondria and they demand a complex chain of biochemicals to ensure proper physiological function. Classically, the blood levels, and not the tissue levels of these metabolites, are determined by expensive and time-consuming biochemical analyses. Since the tissue mitochondria are the consumers of the substrates of glycolysis and of fatty acid metabolism, their redox state is a unique accessible monitor of tissue metabolism and its blockade due to toxins.