The study was conducted on 155 female Wistar rats (aged 3 months, body mass--180-200 g), in diestrus phase of the sexual cycle. The effect of the pineal hormone melatonin (MT) on morphological organization of the follicular apparatus and the vasculature of the ovaries was studied in rats after overheating achieving a rectal temperature of 43.5 degrees C. It was found that hyperthermic exposure lead to an increase of the relative areas of the arteries, veins and lymph vessels of the ovaries. Overheating caused disturbances of folliculogenesis. The injection of MT after exposure to hyperthermia resulted in a quick (already on Day 7 after exposure) recovery of the disturbances of the venous circulation and lymphatic drainage of the ovary, as evidenced by the normalization of the relative sizes of arteries, veins and lymphatic vessels of the ovary, reaching control values. This, in turn, contributed to the reduction of morphological disorders of folliculogenesis and created the conditions for accelerated recovery of the relative area of generative elements of the ovary (at the stages of primary, preovulatory and atretic follicles) as early as 7 days after hyperthermia.