Aim of this study was to evaluate the effects of total thyroid resection on the exocrine pancreatic ultrastructure in both early and late stages of hypothyroidism in experiment. Material and Methods -The experimental study was carried out on 40 mature white male rats of weight 180 to 200 g divided into two groups: group I -intact rats, which were kept in normal vivarium conditions (control group) and group II with experimental hypothyroidism modelled by total thyroidectomy. At the 14 th and 100 th day after thyroidectomy the animals of both groups were sacrificed under thiopental sodium anesthesia and samples of pancreatic tissue were prepared for electron microscopic study.Results -The study of exocrine pancreatic parenchyma showed the diversity of the cellular composition. Light and dark cells were visualized in animals of the control and experimental groups. It was associated with different stages of the cellular secretory cycle. The number of zymogen granules of was sharply reduced in the apical poles of secretory cells, and were completely absent in some cells. Conclusion -The data obtained indicate violations of the ultrastructural organization of pancreatic acinocytes at the early stage after surgery (14 th day). The prolongation of hypothyroidism state (up to 100 days) leads to a number of changes in all structural components of secretory cells that affect the functional activity of acinocytes. Further existence of hypothyroidism is accompanied by the development of dystrophic processes.Cite as Ostapenko OV, Kriventsov MA, Shramko YI, Yermola YA, Mostiuk EM. Electron microscopic study of changes in pancreatic exocrine secretory cells in both early and late stages of hypothyroidism.