Measurements of muscle temperature were performed during and after contractions of human skeletal muscle using an electromyography-needle-electrode, which contains a thermo-element. The investigations aimed at explaining a drop in temperature during contraction, earlier described, and getting some aspects of possible employment of temperature measurements carried out simultaneously with electromyography. 1. The course of temperature during contraction (increase or decrease) depends on the heat of contraction, blood flow through muscle, penetration depth of the thermoelement, gradient of temperature and efficacy of a compression of blood vessels. It results from a superimposition of the single effects. 2. A decrease in temperature in various extremity muscles during contraction is explained by a compression of blood vessles caused by the shortening of muscle, as described earlier by other authors. 3. The interpretation of temperature curves, especially the quantitative interpretation, becomes very uncertain because of various sources of error. A differentiation between muscle heat and influence of blood flow is not sufficiently possible. 4. Nevertheless measurements carried out under conditions of disturbed blood supply, myopathies and polyneuropathies consistent with experiments performed during cooling and warming muscle in a water-bath, causing a reactive hyperemia or a defective circulation by using a blood pressure instrument show that changes in blood circulation are expressed by changes in temperature curves. Measurements carried out simultaneously on agonists and antagonists show satisfactorily the contrary changes in blood circulation known from the literature.