The ability of a cutting fluid to reduce the temperature at the chip-tool interface in the machining of metals is of utmost importance to long tool life. This ability depends, in part, on the heat-transfer properties of the fluid. This paper describes a simple technique for evaluating the heat-transfer properties of fluids. An alternating current of about 50 amp heats the walls of a length of stainless-steel hypodermic tubing while fluid is forced through it at a constant rate. Thermocouples brazed at intervals to the outside of the tube wall measure the wall temperature from which heat-transfer data are derived.