An analysis has been carried out with the aim of clarifying the effects of diffusion thermo and thermal diffusion on heat transfer, flow, and mass transfer for the helium-air boundary layer in stagnation flow. To provide information applicable to both laboratory-type situations and aerospace applications, results have been obtained over the range of free-stream temperatures from 500 to 5000 deg R. For ratios of wall-to-stream temperature (Tw/Te) which differ only moderately from unity, it is found that the aforementioned diffusional transport has a decisive effect on heat transfer. For example, the heat transfer may be from the fluid to the wall even if Tw > Te. Further, the diffusion thermo is far more important than the thermal diffusion. When Tw /Te is much less than unity (highly cooled wall), the diffusional effects on heat transfer are small. For the condition of the adiabatic wall, the surface temperature (adiabatic wall temperature) can exceed that of the free stream by an appreciable amount. Once again, it is diffusion thermo which is responsible for this. Numerical results are given over a wide range of blowing rate for the Nusselt number, friction factor, and helium concentration at the wall.