A pre-, intra- and post-operative determination of thyroid hormone in values in the peripheral and thyroid vein reflux blood of patients with thyroid disorders requiring surgery showed that the so-called intraoperative squeezing of the gland either does not place or is of little importance when delicate surgical movements are commenced. A low incidence of intraoperative arrhythmia was also noted. Prevention of the latter is not indicated, since it is often dependent on surgical movements and/or unorthodox anaesthesiological management.