Abstract
A cytochemical method for the demonstration of endogenous de-hydrogenase activity, i.e. as exhibited in the absence of added substrates, is described in spermatozoa of bull, man and rabbit. This activity is confined to the mitochondrial sheath of the flagellum, and decreases both with spontaneous ageing of sperm and under the influence of certain physical and chemical factors. The method can be applied in spermiology for experimental and diagnostic purposes.