Acrylonitrile-butadiene-styrene was blended in polycarbonate using a twin-screw extruder, producing dispersed and co-continuous blends. The blends were injection moulded into test bars. These materials were tested in single edge notch tensile tests as a function of test speed over a test speed range of 10(-4)-10 m s(-1) (2.85 X 10(-3)-2.85 X 10(2) s(-1)). Infrared measurements were made to monitor the temperature development in the material during fracture. The fracture energies were higher at high test speeds than could be expected based on the low speeds results. This effect was due to an increased fracture stress, initiation strain, and propagation strain. With infrared measurements a temperature increase of 30-40 degreesC was observed. Also the size of the deformation zone increased with test speed. A possible explanation is a thermal blunting resulting from adiabatic heating at high speeds. The brittle-ductile transition temperature increased linearly with the logarithm of the strain rate by a factor of 18.6. At high test speeds the brittle-ductile transition developed with the formation of shear lips.