During thoracic duct drainage a significant decrease of serum beta- and gammaglobulins can be found. 2. The withdrawn lymphprotein can be sufficiently substituted by human serum albumin. 3. The number of small lymphocytes decreases significantly during thoracic duct drainage, while the number of large lymphocytes and lymphoid cells increases. 4. The drainage of thoracic duct in humans is a highly immuno-suppressive procedure without major risks.