In dogs, the thoracic duct lymph has been the object of investigation in studies of gastrointestinal physiology, portal hypertension, experimental pancreatitis, and lymphatic circulation. 1–11 Since the discovery of the role of the thoracic duct as a major pathway in the continuous recirculation of immunologically competent lymphocytes, it has been used to sample and study the pool of this important cell. In this connection also, thoracic duct drainage for the purpose of lymphocyte depletion has been utilized in homotransplantation experiments. Most studies have been performed via an external thoracic duct fistula, however techniques for cannulation of the thoracic duct which allow for repetitive sampling of a dynamically intact lymphatic circulation over a prolonged period of time and without loss of lymph have also been designed.