The following effects were noticed when lymph was drained from the thoracic duct of four patients with severe myasthenia gravis. (1) A pronounced improvement in the myasthenic symptoms was seen after 1–4 days of drainage. In one patient (G. K.) an almost complete remission was seen and the dose of anticholinesterase could be markedly reduced. (2) When the lymph drainage was discontinued the myasthenic symptoms increased again to about the same level as before the drainage. (3) The myasthenic symptoms returned rapidly when the patients own cell-free lymph was retransfused. (4) The lymph drainage did not seem to affect the further course of myasthenia gravis.