The electrical and mechanical activity of the smooth muscle of the guinea-pig prostate gland was studied. The electrical activity of the cells was recorded intracellularly. The resting membrane potential was about -50-60 mV. The majority of cells was electrically quiescent but some cells generated action potentials spontaneously in the normal solution. The repetitive stimulation evoked the excitatory junction potentials and an action potential in some cells. The repetitive stimulation produced the phasic contraction and the response was frequency-dependent. Adrenaline, noradrenaline, and phenylephrine (5 X 10(-7) - 5 X 10(-6) g/ml) exhibited an excitatory effect on the mechanical activity. The frequency of the spontaneous action potential was increased by these agents. The spike number and the duration of the action potential were increased by these drugs. The excitatatory action of adrenaline on the mechanical activity was antagonized by phentolamine. The mechanical responses produced by repetitive stimulation were inhibited by tetrodotoxin and phentolamine but not by propranolol. Atropine and d-tubocurarine did not inhibit the mechanical responses. Tetraethylammonium ions (TEA), at low concentrations, potentiated the mechanical responses. The excitatory action of TEA on the mechanical response was dose-dependent. The frequency of the action potential was increased by TEA. The potentiated mechanical responses obtained in TEA were inhibited by phentolamine but not by propranolol. These findings indicate that the smooth muscle cell of the prostate gland has alpha-excitatory receptors on the cell membrane and the sympathetic neuromuscular transmission is potentiated by TEA.