Prostaglandin (PG) F 2 α , a well known agonist of smooth muscle, is produced in the male gonad. We have investigated whether PG F 2 α stimulates seminiferous tubule contractility through direct action on peritubular myoid cells. Myoid cells from prepubertal rats were highly purified through Percoll density gradient and cultured in vitro. Stimulation with PG F 2 α was observed to induce: (i) rapid and dose-dependent production of inositol phosphates; (ii) mobilization of Ca 2+ from intracellular stores and (iii) cell contraction. Moreover, at a concentration of 10 μM the agonist was found to induce immediate contractile response of peritubular tissue in freshly explanted tubular fragments from both young and adult rats; the explants were examined in whole-mount preparations and the peritubular myoid cell layer was identified by selective staining for alkaline phosphatase activity. Our observations demonstrate that myoid cells are a direct target for PG F 2 α and suggest a role of the eicosanoid in the intragonadal control of seminiferous tubule contractility.