A semi‐quantitative method for studying the composition dependence of the non‐Newtonian melt viscosity of commercial grades of polypropylene‐linear‐polyethylene blends is presented and its effectiveness illustrated with data for two sets of blends differing widely in the molecular weight of the components. The usefulness of the composition dependence of the molten blend's specific volume in gauging their rheological behavior is also demonstrated. Melt elasticity is estimated from extrudate swell. A technique is developed for estimating the influence of the blends composition on their melt elasticity in the nonlinear range. This technique is proposed as an extension of the relaxation spectrometry widely employed for the study of solid polymers. Finally, the terminal zone of the relaxation spectra for the blends is determined from dynamic measurements using the Weissenberg rheogoniometer.