The effect of injecting a secondary gas stream through a rear ward-facing slot in a direction parallel to a wall into a supersonic air flow has been examined in a small Mach 3 wind tunnel. The experiments were carried out for three step heights, 0.121, 0.180, and 0.239 in. with slot openings of 0.064, 0.123, and 0.182 in., respectively. Air was used as the secondary fluid with these three different slot openings. The total temperature of the main flow was equal approximately to the room temperature, and the temperature of the wall at the point of injection varied between 418° and 655°R as determined by the temperature of the secondary air. The ratio M of the mass velocity in the secondary stream to that of the mainstream was in the range of 0 to 0.408. Helium also was injected through a slot opening of 0.063 in. for two different injection parameters M = 0.01 and 0.02 and a temperature of the wall at the point of injection ranging between 562.8° and 663.7°R. Schlieren photographs are presented and adiabatic wall temperature measurements are described.