The viscosity of road bitumen is a rational, physical property which plays an important role in the technological and quality assessment of a binder. On the other hand, it is believed that the viscosity might substitute for the penetration of a bitumen as a classification property in the appropriate standards. Measurement of the bitumen’s viscosity at lower temperatures, e.g. 60°C, creates some problems caused by the non-Newtonian character of the material. This is observed when dealing with hard bitumens and particularly with polymer-modified bitumens (PmBs). This paper presents viscosity measurements of three PmBs with a rotational viscometer. Regression analysis of the results was conducted according to the four-parameter Cross model, which enabled calculation of the absolute viscosity (or zero shear-rate viscosity). The computed flow curves according to the Cross model were compared with those according to the power-law model frequently applied for road bitumens. The calculated absolute viscosity values together with the conventional test results were applied to the Heukelom bitumen test data chart.