The state of physiological functions of the whole organism, its vital activity and adaptation to various changes in the surrounding and internal environment is controlled by neurohumoral mechanisms. The main place in the implementation of those mechanisms belongs to hormones. A clinically relevant problem is currently the relationship between activity of thyroid gland and prolactin. Aim of study. - To elucidate further the relationship of thyroid-stimulating hormone, thyroxine and prolactin. The study was performed on virgin 30 mature male mice and 33 mature female mice of the inbred line C3H-A. On male and female mice was reproduced a model of experimental hyperthyroid and hypothyroid status by the administration to L-thyroxin and propylthyouracil, accordingly. The blood samples from animals were assayed for TSH, T4 (total) and prolactin. In the hyperthyroid male mice the level of T4 (total) was significantly higher as compared to the hypothyroid and control groups. No deference for the level of TSH and prolactin was found between the hyperthyroid and the hypothyroid groups. In the hypothyroid female mice the level of TSH and T4 (total) was significantly lower and the level of prolactin was significantly higher as compared to the hyperthyroid and the control groups. The male and female mice responded in different ways upon the administration to L-thyroxin and propylthyouracil on the level of TSH, T4 (total) and prolactin.