To evaluate the possible antigoitrogenic effect of somatostatin, the influence of long-acting somatostatin analog--octreotide--on experimental goiter developed in rats treated with propylthiouracil was examined. Goiter formation was assessed by measurement of the main histological compartments of the thyroid as well as by morphometric analysis of the vascularization and blood supply of the gland. Although treatment with octreotide did not prevent the goiter formation, it clearly reduced blood supply and vascularization of the thyroid and counteracted propylthiouracil-induced increase in the relative volume of follicular epithelium. To conclude, the somatostatin analog--octreotide--is effective in reduction of goiter vascularisation. This finding provides a rationale for the clinical trials of the treatment of hypervascular goiter by somatostatin analogs.