An experimental investigation of turbulent flow over a cavity in an aerodynamic surface has been conducted. The test was carried out at nominal Mach numbers of 4 and 8, with Reynolds numbers based on free-stream conditions and length of body ahead of the cavity of 8.0 x 10 to the 6th power and 11.0 x 10 to the 6th power, respectively. Two conditions of wall-to-free-stream stagnation temperature ratio, 0.4 and 0.8, were tested at M(inf) = 8.09, whereas at M(inf) =3.99, the temperature ratio was 0.75. For all tests, the ratio of initial boundary-layer thickness to cavity depth was approximately 0.2. Measurements were made of surface pressure and temperature, and flow field surveys of pitot and static pressures and total temperature were performed. The test results showed that the recirculating fluid temperature was not less than 0.7 times the free-stream stagnation temperature despite decrease of the wall temperature to 0.4 the free-stream value. A satisfactory correlation was obtained between the experimental velocities and the error function profile of Goertler, and the distribution of total temperature across the mixing layer was adequately described by Crocco's linear relation of total temperature and velocity. A value of the mixing coefficient near 12 was found regardless of Mach number or wall- to-free-stream stagnation temperature ratio.