The modalities for the heterotopic transplant of heart-lungs in the rat are described in detail. As in the case of all other rat transplants, this type is fairly easily performed using the techniques and instruments of microsurgery. Special attention is required at the moment of isolating the heart-lung preparation, at perfusion of the coronary circulation and with respect to the exact positioning of the heart-lung block in the abdomen of the recipient. The experimental model may be used for strictly immunological researches or for physiology, pharmacology and haemodynamics research.