Laser holographic interferometry was applied to the measurement of density profiles of two-dimensional planar turbulent boundary layers on the wall of the Acoustic Research Tunnel (ART) at the Arnold Engineering Development Center (AEDC). Holograms were produced at Mach numbers 0.50 and 0.65 by the finite fringe, single-plate, dual-exposure method. The reconstructed image from this type of hologram contains fringes that are shifted relative to a reference fringe by an amount that is proportional to the difference in the densities at the two points. Therefore, it was possible to determine the density profiles by measuring the fringe shifts appearing in the reconstructed images. The results of two velocity-temperature relations are presented, and compared to data obtained by pitot, hot-wire, and split-film probes. A description of the experimental facility, hardware for data acquisition, data reduction methods, and a discussion of the problems encountered in the holographic interferometry technique are presented.