The method of construction and operating conditions are given for a respirometer suitable for determining steady‐state rates of oxygen uptake by peripheral nerve. The polarographic method is used to measure the change in oxygen concentration occurring when a solution of known oxygen concentration flows at a constant, predetermined rate over a tissue sample which removes oxygen from the stream. From a knowledge of the concentration change and volume‐flow rate the rate of oxygen uptake by the tissue is readily determined. Electrodes for stimulating the nerve sample and for recording the action potential are provided. By virtue of the flow system the respirometer maintains constant environmental conditions. The system is linear with respect to changes in the steady‐state rate of oxygen consumption, and the sensitivity is such that, for a 10‐mg sample of nerve, changes in the rate of oxygen uptake of 0.1 micromoles/g hr., (2 cu. mm/g hr.) are readily detected.