The correlation between low‐shear Newtonian melt viscosity and polymer molecular weight distribution in the high molecular weight region is inspected via the viscosity of homologous binary blends. It is confirmed that viscosity depends uniquely upon the weight average molecular weight and no other moment. The work of Peticolas and Menefee is extended in order to show certain previously reported theoretical predictions to be inconsistent with the data, at least for molecular weight distributions of the type produced by previously defined blends. Nine sets of viscosity vs. composition data are compared. The blends cover a wide range of polydispersity for high molecular weight poly(dimethyl siloxanes) and polystyrenes. A viscosity vs. molecular weight curve for poly(dimethyl siloxane), reduced to 25°C, is compiled from eight independent sets of literature data.