A hot-tool welding machine was used to study the weldability of unfilled and 30 wt% glass-filled poly(butylene terephthalate). For each of these materials, 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. It is shown that very high weld strengths can be achieved in the unfilled material. In the filled material, weld strengths comparable to those achieved by vibration welding are shown to be achievable. (C) 2000 Elsevier Science Ltd. All rights reserved.