An exploratory analysis has been developed for the case of distributed injection of a foreign gas into a turbulent boundary layer in air on a flat plate. The work is divided into three parts: a derivation of the basic turbulent boundary-layer equations for a binary gas system; a derivation of modified Reynolds analogies between momentum, mass, and heat transfer for a binary gas system; and an evaluation of the effect of foreign gas injection on the skin friction and heat transfer of a nearly isothermal boundary layer by means of mixing length theory. Numerical results are presented for the injection of hydrogen and helium into the boundary layer for a temperature of 500 degrees R. It has been found that the injection of a given mass of light gas is much more effective than the same mass of air in reducing skin friction and heat transfer on the flat plate. The same reductions are generally achieved with about 20 percent as much hydrogen and about 40 percent as much helium as in the case for air.