Testes of prepubertal, pubertal and adult Wistar rats were stimulated with low-intensity pulsed ultrasound for 20 min a day, for 7 days. No significant changes were found in the spermatogenic activity as well as in plasma LH and FSH levels following ultrasound treatment. The testicular androgenic activity, however, was significantly increased in prepubertal treated animals, in addition to a significant increase in seminal vesicle growth and secretory activity. In spite of normal androgenic levels, pubertal treated rats presented also an increase in the seminal vesicle secretory activity, thus suggesting a direct action of ultrasound on the gland.