The electric potential across the membrane (psi) is evaluated through the accumulation of the lipophilic, radiolabelled, triphenylmethylphosphonium (3H-TPMP+), cation on membrane human sperm. The washed sperm cells, were incubated in presence of 3H-TPMP+ in low-K+ medium or high-K+ and allowed to take up the cation to steady-state (ie; 20 min at 37 degrees C). By using this differential, the value obtained was inserted in the Nernst equation, this value yielded a psi of -69 +/- 2 mV. The presence of divalent cations Zn++ and Mg++ in the incubation medium both induced a hyperpolarization of 10% and 8.6%, respectively. The addition of specific reagents such as p-chloromercuribenzene-sulfonate and ethylene-diamine-tetraacetic acid sodium salt both decreased the psi 35% and 58% respectively. The agents to act upon the components of the sperm cell membrane such as the dithiothreitol and progesterone induced hyperpolarization and depolarization of the membrane 16% and 40%, respectively. The presence of propranolol and L-alpha-lysophosphatidylcholine, which affect the ionic gradients present across the plasma membrane, both induced a depolarization from 43% and 92% respectively. Finally, the addition of tetraphenylboron (TPB-) on the incubation medium, enhanced the value of the psi 75%. These studies are transcendent because with the utilization of agents depolarizing, or hyperpolarizing we obtain changes in the psi from -80 +/- 0.6 mV, until -6 +/- 0.6 mV changes of 74 +/- 1.5 mV across of the sperm cell membrane.