SummarySerial plasma long‐acting thyroid stimulator levels are documented for five patients with thyrotoxicosis who had L.A.T.S. in their plasma and developed P.T.M. during the course of their disease. In all cases it was found that exacerbation of the patient's shin lesion was associated with a rise in L.A.T.S. and a remission, whether spontaneous or therapeutically induced, with fall in L.A.T.S. The development of P.T.M. in the shin graft donor site on the thigh of one of these patients is described and is shown to be associated with a rise in L.A.T.S. These results strengthen the hypothesis that L.A.T.S. may be the direct cause of P.T.M., probably by reacting with an antigen in the shin tissues. It is further suggested that surgical trauma may be one of the local factors which is a predisposing factor in the occurrence of the conditio