The lymphatic system plays an important role in the body circulation, but our methods for studying the system in the living organism are limited, and its physiology is incompletely understood. Kinmonth6,7 introduced lymphangiography, a method for visualization of the lymph vessels in the extremities by injection of contrast medium directly into the cannulated lymph vessel. With lymphangiography, pathological changes in the lymph vessels such as varicose lymph vessels or decrease in number of lymph vessels were demonstrated in lymphedema. The decreased capacity for flow in the lymphatic system was then explained. A method for estimation of lymph flow in the extremities would be valuable for studying this decrease, and therefore the following experimental study was performed. On the assumption that substances with the molecular size of albumin or larger are solely removed from the extravascular space by the lymphatic system, radioactive iodinated human serum albumin (RIHSA) was injected into