As the use of biodiesel becomes more widespread, engine manufacturers have expressed concern about biodiesel's higher viscosity. In particular, they are concerned that biodiesel may exhibit different viscosity-temperature characteristics that could result in higher fuel injection pressures at low engine operating temperatures. This study presents data for the kinematic viscosity of biodiesel and its blends with No. 1 and No. 2 diesel fuels at 75, 50, and 20% biodiesel, from close to their melting point to 100 degrees C. The results indicate that while their viscosity is higher, biodiesel and its blends demonstrate temperature-dependent behavior similar to that of No. land No. 2 diesel fuels. Equations of the same general form are shown to correlate viscosity data for both biodiesel and diesel fuel, and for their blends: A blending equation is presented that allows the kinematic viscosity to be calculated as a function of the biodiesel fraction. Paper no. J9166 in JAOCS 76, 1511-1513 (December 1999).