The thyroid gland is of great importance because of the synthesis and secretion of hormones which play key roles in the maintenance of animal physiology. In this context, the aim of the present study was to determine morphometric parameters of thyroid structures subjected to infrared laser stimulation (ILS) and for this purpose, 10 Sprague Dawley rats, 3 months of age and weighing approximately 200 grams, were divided into two groups of 5 animals each: the control group and the remaining 5 animals constituting the experimental group received infrared stimulation in the thyroid with doses of 16 J/cm2 for 15 consecutive days. After the rats were sacrificed, the respective thyroids were removed and processed for optical microscopy. Histological plates and micrographs were obtained with final increases of up to 1000 X. Morphometric studies were carried out to determine the tissue variations generated by infrared inductions, with special emphasis on the colloidal arrangement and dimensions of follicles and thyroid cells. Our results revealed that there are marked differences in all the components of the analyzed thyroid tissue which could give antecedents of different functionalities in the metabolism of thyroid glands.