Abstract: A two-stage refrigeration system including a primary cooling circuit which may be of the mechanical, vapor-compression type and a secondary closed system which is limited to an evaporator, located in the product storage area, a condenser and the necessary interconnecting conduits. The two circuits are operatively linked by a heat exchanger located outside the product storage area. The heat exchanger serves as the evaporator of the primary, caustic refrigerant system, and as the condenser of the secondary, relatively safe, volatile refrigerant system. Means are provided to prevent the refrigerant of the primary circuit from entering the secondary circuit in the event of heat exchange leakage. The heat exchanger design as well as the primary circuit control permits a rapid response to changes in temperature in the product storage area without requirement of controls on the secondary side of the system.