The technique of pulmonary lymphoscintigraphy was used to evaluate pulmonary lymphatic flow and to assess reestablishment of lymphatic drainage after lung transplantation. A first group of six control dogs underwent percutaneous transthoracic injection of a radiocolloid into the periphery of the left upper and lower lobes. Radiocolloids are large molecules tagged with radioisotopes that are absorbed only through lymph and are concentrated in tributary lymph nodes. Twenty-four hours after injection the dogs underwent scintigraphic studies of the chest and upper part of the abdomen. Mediastinal lymph nodes were visualized in all animals. A second group of four dogs underwent partial reimplantation of the native left lung, with interruption of all lymphatic connections between the lung and mediastinum. Lymphoscintigraphic studies of the left lung were obtained on the third postoperative day and then weekly for 4 weeks. Three of the four dogs in this group did not have visible mediastinal nodes 3 days after the operation. Nodes were visualized in all animals at 1 week and at all following studies. A third group of five dogs were subjected to left lung allotransplantation by means of standard surgical techniques, as well as immunosuppression. The animals were studied with radiocolloid injections and lung lymphoscintigraphy at weekly intervals for 6 weeks. Mediastinal nodes were visualized for the first time 2 to 4 weeks after the operation and at every subsequent study. We conclude that lung lymphoscintigraphy is a reliable technique for the study of pulmonary lymphatic flow. This experiment demonstrates that lymphatic drainage after lung transplantation is reestablished as early as the second postoperative week. (J Thorac Cardiovasc Surg 1993;106:167-71)