The flow behavior of polycarbonate (PC) blended with three kinds of polyolefins (LDPE, HDPE, PP) was studied at 260°C using an Instron Capillary Rheometer. Flow behavior of the blends was found to be very different from that of the individual components, and significant viscosity reductions were observed for blends consisting of 5% and 15% polyolefins. In particular, the viscosity of PC/HDPE was found to be much lower than that of the parent viscosity at a shear rate below 100 1/s. For pure components, a crossover of PC viscosity was observed at high shear rate for HDPE and PP. Interfacial slippage in the blends has been suggested as the flow mechanism by which a substantial reduction in the melt viscosities of either component takes place upon the addition of a small amount of the other. A new method was proposed to evaluate the relationship between the characteristic slip factor of the blend and the viscosity of the mixture. A single master curve was obtained, i.e., σm/αAB = a · p±b, where σm is the shear stress at the matrix, αAB the slip factor, p the viscosity ratio, and a, b the constants. © 1994 John Wiley & Sons, Inc.