The increase in respiratory activity in germinating peanut cotyledons has been correlated with an actual increase in mitochondria. Using sucrose gradient centrifugation, it was shown that succinoxidase activity is associated with a well-defined band of cell particulates of uniform density, size and ultrastructure. During germination the population of succinoxidase-containing particles increases, as shown by enzymatic assay, protein assay and direct particle counts with the phase contrast microscope.