Effects of ionizing radiation in doses 0.5 and 1 Gy on triiodothyronin reception by rat peripheral blood lymphocytes were examined 3, 10, and 30 days after exposure. Binding capacity of 125-I labeled triiodothyronin by lymphocyte receptors was found to change depending on the dose of external irradiation and time elapsed since the exposure. The most marked and earliest changes in the parameters of hormonal-receptor interaction were observed after irradiation in dose 1 Gy.