Vibration welding is used to assess the weldability of poly(butylene terephthalate) (PBT) and a polycarbonate/poly(butylene terephthalate) blend (PC/PBT) to each other and to other resins and blends: PET to PC/PBT, PET to modified poly(phenylene oxide) (M-PPO), PET to polyetherimide (PEI) and PEI to a 65 wt% mineral-filled polyester blend (65-PF-PEB), PET to a poly(phenylene oxide)/polyamide blend (PPO/PA), PC/PBT to M-PPO, and PC/PET to PPO/PA. Based on the tensile strength of the weaker of the two materials in each pair, the following relative weld strengths have been demonstrated: PET to PC/PET, 98%; PET to PEI, 95%; 65-PF-PEB to PEI, 92%; and PC/PET to M-PPO, 73%. PET neither welds to M-PPO nor to PPO/PA, and PC/PET does not weld to PPO/PA.