Three grades of bisphenol-A polycarbonate-high molecular weight linear, high molecular weight branched and low molecular weight linear-and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agreed with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The T-g of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory-Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power-law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox-Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle-ductile transition at ca -30 degreesC and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched Izod test caused the impact strength at room temperature to decrease almost linearly with blend composition.