The need of developing a continuous method of recording the volume-flow of blood for the study of disturbances in circulatory equilibria was pointed out. A thermo-electric method was described, based on the principles of heat transfer between two circulating fluids of different temp. The circulating blood of a heparinized dog was exposed to a constant flow of water in a concentric water jacket. Changes in differences of temp. between the inflow and outflow of water were recorded by a sensitive thermopile. The relation of E. M. F. to flow of blood was established in experiments on ox blood for different temp. gradients between the circulating blood and circulating water (in vitro). Such calibration curves used for analysis of records from animal experiments were steeper with the larger temp. gradients and at the lower blood flows. The relation of these points to the sensitivity and accuracy of the method were discussed.