A method of obtaining an extract of soluble enzymes from pea seedling mitochondria is described. Evidence is presented that the mitochondrial extract contains the following enzymes: Diphosphopyridine nucleotide (DPN) and triphosphopy-ridine nucleotide (TPN) specific wocitric dehydrogenases, alcohol dehydrogenase, formic dehydrogenase, aldehyde dehydrogenase, glutamic dehydrogenase, malic enzyme, lactic dehydrogenase, fumarase, aconitase, DPN and TPN cytochrome-c reductases, adenylate kinase, phosphopyridine nucleotide transhydrogenase and oxaloacetic carboxylase. The relative activities of these enzymes have been quantitatively determined and the results discussed.