Abstract: A portable, thermally insulated container having an isothermal chamber for storing temperature sensitive material. An electronic circuit activates a heater when the temperature in the chamber is below a preselected magnitude and activates a Peltier heat pump to cool the chamber when the temperature in the chamber is above a preselected magnitude. The electronic circuit operates a fan for the intake of air into the chamber while the Peltier heat pump is operating and discontinues the operation of the fan while the heater is operating. Included in the electronic circuit are two sets of dual operational amplifiers. A temperature sensor responsive to the temperature in the chamber controls the operation of one set of dual operational amplifiers for operating the Peltier heat pump to cool the chamber and controls the operation of the other set of dual operational amplifiers to heat the chamber.