In view of the existence of a different secretion pattern of growth hormone (GH) between male and female rats, the aim of the present study was to analyse the role played by ovarian steroid hormones in the modulation of such secretion. To do so, postpubertal female rats were ovariectomized and killed at 30 days after the operation. The basal serum levels of growth hormone together with cell area, cytoplasmic area and nuclear area of the hypophyseal somatotropic cells of normal and ovariectomized rats were compared. The results obtained show that ovariectomy induces a significant decrease (p less than 0.05) in the basal serum levels of GH, accompanied by an increase in cellular and cytoplasmic areas, with no significant differences in nuclear area. Ovariectomy was also accompanied by an increase in reaction intensity and the number of GH-immunoreactive cells (p less than 0.01). These findings point to the shift towards a masculine secretory and morphological pattern following ovariectomy and supports the hypothesis that ovarian steroids intervene in the establishment of a different pattern in females compared to males.