Stagnation‐point similarity solutions of the laminar boundary‐layer equations are calculated for a thermally and calorically perfect gas with Prandtl number ⅔ and viscosity proportional to a power of the absolute temperature (&mgr; ∝T1−&agr;). The parameter &agr; is varied from 0 to 0.5, and the enthalpy ratio across the boundary layer from 0.01 to 0.80. The results are closely applicable to high‐temperature flows of the five inert gases. Heat‐flux values predicted using these results and Amdur and Mason's viscosity calculations are compared with Rutowski's shock‐tube measurements for argon. The agreement is excellent up to a stagnation temperature of 5400 °K. At higher temperatures, the experimental values gradually rise above the theoretical curve, indicating possible onset of electronic excitation and ionization effects upon the heat transfer.