The Doolittle approach to Newtonian viscosity assumes &eegr;=AexpB/f, whereAandBare constants independent of temperature andf, the relative free volume, is (v−v0)/v0. Herevis the specific volume andv0is the occupied volume. Using machine computations, this equation was applied to published data on polystyrene, replacingvby its equivalentvg+(dv/dT)(T−Tg), wherevgis the specific volume at the glass temperatureTg. The agreement between calculated and observed viscosities is at least as good, and perhaps better, than that afforded by other existing empirical expressions. The constantBis independent of molecular weight and temperature whilev0depends slightly on molecular weight. A log‐log plot ofAagainst molecular weightMproduces two straight lines intersecting atM=35 000. At higher values ofM, the slope is 3.4; at lower values, it is slightly greater than one. This treatment separates the melt viscosity of polystyrene into two factors,A, dependent only on structural parameters, andf, which is determined by the specific volume and is a function of temperature.