In single-screw extrusion it is not unusual to encounter large temperature variations within the screw channel, especially at high pumping rates. These temperature variations result in nonhomogeneities that affect the quality of the final product. Although there have been numerous efforts aiming at the simulation of the flow in the channel of a single-screw extruder, and the prediction of important flow quantities, there is hardly any published work in which the temperature distribution in the screw channel was actually measured. Such measurements, if available, would provide data by which computer simulations could be validated. In the present study, a fast-response, cam-driven thermocouple system was developed and used to measure the radial temperature distribution in the screw channel. The measurements are carried out on a well-controlled, custom-built, single-screw extruder. Temperature profiles in the centerline of the screw channel were obtained for various operating conditions of the machine. The data obtained revealed interesting features of the flow as well as the dominant heat transfer mechanisms. The system as developed here can be improved to accommodate larger industrial applications.