A hot-tool welding machine was used to study the weldability of polyetherimide, a high-temperature amorphous thermoplastic. Weld strength data are reported for two specimen thicknesses. In these experiments, the outflow in the melting phase was controlled by means of stops, the thickness of the molten film was controlled by the heating time, and the outflow during the final joining phase was also controlled by displacement stops. Strength data for butt welds are reported for a series of tests in which the hot-tool surface temperatures, the heating times, and the displacement stop positions were varied, but the pressure was not. Within the range of the weld process parameters investigated, the highest weld strength achieved was of the order of 85% of the base strength of the material. This is lower than the 100% weld strength that can be achieved in this material by vibration welding.