With the increasing importance of process simulation in the field of plastics processing, the accurate material data measurement also gains importance, because the reliability of those simulations is based on the accuracy of the material data. This means not only to consider the temperature dependency of the material data, but also a possible pressure dependency. The aim of this thesis was the determination of pressure and temperature dependent the viscosity and the thermal conductivity for a PC/ABS-blend and a pure PC. For the viscosity measurements a so-called, at the Institute for plastics processing developed, injection moulding machine rheometer had been used. The results of the viscosity measurements were strongly influenced by viscous dissipation. For the investigated blend, this heating effect caused thermal degradation of the material in the injection moulding machine rheometer. In consequence, the measurements had to be carried out again in a high pressure capillary rheometer, which was adapted with a back pressure chamber. In order to compensate these heating effects, a temperature correction was necessary for the measured viscosity values. For this correction, the required actual melt temperatures were calculated out of the wall temperatures by using the Agassant method. Due to the large pressure drops in the die this method had to be enhanced, to account the melt decompression. The results of the temperature calculation showed, in the case of the injection moulding machine rheometer (uncorrected apparent shear rate range from 250 s-1 to 3500 s-1), an increase in the average melt temperature up to 30°C compared to the test temperature. The maximum melt temperatures were up to 50°C higher than the test temperatures. In the high pressure capillary rheometer with the round die (uncorrected apparent shear rate range 250 s-1 to 10000 s-1) the temperature rises were smaller, up to 15°C for the average and up to 25°C for the maximum melt temperature. The pressure coefficient, which describes the pressure dependency of the viscosity, was 23.6 GPa-1 for the PC/ABS-blend and obtained a value of 33.1 GPa-1 for pure PC. The thermal conductivity measurements, based on the line source method, were carried out on an adapted high pressure capillary rheometer. An interesting aspect was, that below the glass transition temperature no increase in the thermal conductivity occurred with increasing pressure. Above the glass transition temperature, a pressure increase of 800 bar resulted in an approximately 10% increase of the thermal conductivity for the blend and 15% for the pure PC. In a separate chapter an enormous potential for further developments of the measurement and evaluation methods, especially for the viscosity measurements, is discussed.