Long-term cannulation of the thoracic duct became a research tool with the advent of plastic tubing materials. However, technical problems still face investigators who try to obtain thoracic duct lymph over a long period of time. In our laboratory, a system capable of obtaining intermittent thoracic duct lymph samples over a ten-day period has been developed. Anatomic Catheter Placement Three anatomic features of the thoracic duct (TD) are pertinent to its successful catheterization: (1) occurrence of multiple communicating collateral branches (Col) near its termination; (2) a bifurcation (Bi) in the main duct in the vicinity of the third and fourth thoracic vertebrae; and (3) multiple lymphatic-to-venous (L-V) connections in addition to the termination of the TD at the junction of the left jugular and axillary veins. Cephalad to the diaphragm, the main thoracic duct gives off several collateral branches (Fig 1-3) which reunite with the main duct at its bulbous