The transport of secretory granules towards the subplasmalemmal (SPL) region of the luteinizing-hormone (LH) gonadotrope is controlled by the LH-releasing-hormone-dependent pathway. The SPL granules contain the most readily releasable LH. To test the effect of diabetes on both the number and LH content of marginated granules, we studied by indirect immunogold-labelling pituitaries from control and streptozocin (STZ)-treated male rats. On electron micrographs we measured the areas of the gonadotrope nucleus and cytoplasm, counted all secretory granules, and counted and measured secretory granules in selected SPL regions. Furthermore, we counted gold particles (IG) on (a) the secretory granules of the SPL regions, (b) the intergranular SPL cytoplasm and (c) the region outside the cell. Finally, in order to evaluate possible diabetes-related changes of the pituicyte cytoskeleton, we measured by densitometry actin, tubulin, vimentin, and desmin in immunocytochemically stained pituitary sections. In diabetic compared with control cells of the studied pituitary region, we observed: (a) cytoplasmic atrophy; (b) the number of secretory granules per unit area increased in the total cytoplasm, and decreased in the SPL cytoplasm (lowered regulated secretion); (c) decreased IG labelling in the SPL granules (reduced amount of hormone transported by each granule towards the cell membrane); (d) decreased IG labelling in the intergranular SPL cytoplasm (reduced constitutive secretion), and (e) strongly increased actin and desmin, yet unchanged tubulin and vimentin immunoreactivity. Our data indicate that both regulated and constitutive secretion are possibly reduced in gonadotropes of diabetic male rats. The cytoskeletal alterations may also contribute to the reduced regulated secretion.