In 100 mature tortoises (Testudo horsfieldi Gray) reparative peculiarities and dynamics of histogenesis of the thyroid gland were studied under the conditions of its partial resection. The most intensive reparative processes were observed on the injured surface of spring--summer group of animals. The source of the thyroid parenchymal proliferation in reptiles are thyrocytes in destroyed follicles, proliferates and intrafollicular islets from the adjacent parts of the organ. During winter season, revascularization and proliferation of epithelium is inhibited, thus resulting in delay of the organ's regeneration. In intact part of the thyroid gland, hypertrophy and hyperplasy of thyrocytes, increasing number of small follicles are observed. This demonstrates compensatory rearrangements of the remaining part of the organ.