A hot-tool welding machine was used to study the hot-tool weldability of several commercial thermoplastic blends: a blend, ABS, of acrylonitrile-butadiene-styrene; a blend, PC/ABS, of polycarbonate (PC) and ABS; a blend, PC/PET, of PC and poly(butylene terephthalate) (PBT); a blend, M-PPO, of poly(phenylene oxide) (PPO) and HIPS; a blend, PPO/PA, of PPO and polyamide 6,6; 30GF-MPPO, a 30 wt% glass-filled grade of M-PPO. Weld strength data are reported for a specimen thickness of 3.2 mm. 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. The maximum relative weld strengths demonstrated are 100% in ABS, 91% in PC/ABS, 98% in PC/PBT, 80% in M-PPO, 100% in PPO/PA and 77% in 30GF-MPPO. A maximum relative strength of 38% was obtained in hot-tool welds of PC/ABS to M-PPO.