Results are presented on the effects of helium in a hypersonic turbulent boundary layer. Helium is injected at sonic speed through a spanwise slot upstream of the measurement location in a fully developed Mach 7.2 turbulent boundary layer. Particle image velocimetry and infrared thermography techniques are used to measure the velocity and temperature fields, respectively. Preliminary results for the mean and turbulent flow field along with the temperature field are presented. The mean field measurements are compared with earlier Pitot tube data and the differences may be due to the assumptions made regarding the fluid properties of the air/injected gas mixture, or due to spanwise variations that remain to be explored.