The selective staining of plasma membranes of plants [Glycine max] and porcine spermatozoa given by a mixture consisting of 1% phosphotungstic acid in 10% chromic acid (PACP) applied following periodic acid destaining of glutaraldehyde-osmium tetroxide-fixed EM sections is reduced or eliminated by prior extraction of the tissues with lipid solvents, including ethanol. The ethanol-soluble fraction of sperm contains constituents which restore the PACP-staining reaction when added to ethanol-extracted and lyophilized sperm. Analysis of the ethanol extracts by TLC revealed 2 major components which reacted with both phosphotungstic acid (PTA) and .alpha.-naphthol detection reagents. These PTA-positive constituents were concentrated in plasma membranes of sperm. Components with similar mobilities were found in fractions of plasma membranes from plants. Addition of the PTA-positive constituents from either sperm or plants to extracted and lyophilized sperm restored the PACP staining. One or more low MW constituents (saccharides or glycolipids), rather than glycoproteins, concentrated in plasma membranes are apparently responsible for the unique PACP staining in both plants and porcine sperm.