Exocytotic process in growth hormone (GH) and prolactin cells (PRL) of the frog anterior pituitary have been examined using an experimental design that has been previously demonstrated to increase the release of hormone from both cell types. Hemipituitaries of the same animals were superfused either with medium alone or containing 100 ng/ml of thyrotropin-releasing hormone (TRH) for 24 hr. PRL and GH cells were identified by the colloidal gold method using anti-human prolactin and anti-ovine growth hormone as primary antisera. In hemipituitaries cultured with medium alone, PRL and GH cells showed few exocytotic figures with different morphology in both cells types. In TRH treated hemipituitaries, PRL cells showed numerous exocytotic vacuoles containing immunoreactive granulated material that was preferentially located near basal lamina. On the other hand, GH cells showed higher amount of exocytotic vacuoles containing heterogeneous immunoreactive material, located along the cell membrane. In PRL cells single secretory granules are secreted, whereas GH cells showed multigranular exocytosis. These results indicate that in PRL and GH amphibian cells exocytotic process has a different polarity and morphology and that this process increases with TRH stimulation.