Ischaemic reduction of tremor size has been attributed to changes in muscle spindle sensitivity (Lippold, 1970). However, an artificially produced tremor (a small movement of the hand produced by repetitive low intensity ~10 Hz electrical stimulation) was also rapidly attenuated by ischaemia (Lakie et al, 1986). Thus the effect appeared less likely to be a reflex action and more likely to be a muscular phenomenon. Here we examine in more detail the effect of ischaemia on human physiological tremor. The tremor experiments were performed on 6 subjects (5 male). Their mean age was 37 years (s.d 9 years). Permission was obtained from the local ethical committee and the written informed consent of the subjects was obtained for these experiments which conformed to the declaration of Helsinki. All subjects declared themselves to be in good health and none had overt neurological symptons or were taking beta agonist of beta blocker drugs. Postural tremor of the right hand was measured by conventional accelerometry and analysed by FFT. Control measurements were obtained and a cuff encircling the right upper arm was inflated to 200 mmHg. Subjects either maintained the posture throughout the ischaemic period or they relaxed the arm. Integrated surface EMG was recorded from the extensor digitorum communis muscle. For all our subjects a substantial reduction in tremor size occurred only when ischaemia was combined with postural activity. The overall reduction in tremor size was large and significant when the ischaemic arm was active (60% reduction s.d. 10%, p0.05) when it was relaxed between measurements. The gross EMG associated with the tremor was not significantly different in the two conditions (p>0.05) (repeated-measures t-tests (Bonferroni Adjusted).In a separate series of experiments analogous measurements were made using low level 8 Hz percutaneous stimulation of the first dorsal interosseus muscle. The size of the resulting sub-tetanic force fluctuation was measured and expressed as a percentage of the mean force. Force fluctuation was significantly reduced by ischaemia (p < 0.05) when stimulation continued throughout the 2 minute ischaemic period, whereas ischaemia on its own had no effect. The effect on both tremor and force fluctuation is consistent with depletion of a substrate or accumulation of a metabolite in muscle.