Zinc normally participates in the stabilization of the chromatin of human spermatozoa, which have a high content of zinc after ejaculation. Sperm chromatin, depleted of zinc with EDTA, regained stability in the detergent SDS after exposure to Cd2+ in vitro. This effect was reversible with EDTA, but albumin could not reverse the stabilization caused by Cd2+ to the same extent as it reversed the stabilization caused by Zn2+.