The experiments were carried out on four adult monkeys (Macaca irus) under pentobarbitone sodium anaesthesia in order to find the effect produced by a local injection of 1:10,000 noradrenaline on intrusive movements of the incisor teeth. This intrusive mobility was measured with a transducer, incorporating silicon strain gauges, while a strain gauge dynamometer was used to apply manual force approximately parallel to the long axis of the tooth. The mobility was assessed periodically by giving five thrusts preceded by intervals of 10 seconds. After two initial series of thrusts a submucous injection of 1:10,000 noradrenaline was given labially and lingually. The mobility was then assessed periodically for several hours. Seven control teeth were studied by injecting 1 ml. of physiological saline.It was found that with injections of noradrenaline the mobility decreased over a period of 1 to 1½ hours and then returned towards its original mobility, whereas no comparable alteration in the intrusive mobility was detected when physiological saline was injected. It is concluded from force‐movement curves that the reduction in the vascular supply to the periodontium which may be presumed to occur substantially reduced the initial movement due to loads below 100 gf (0.981 N) and caused a progressively greater reduction as the load increased to 250 gf (2.451 N).