A dark‐field oscillatory spark microphotography technique has been developed to study with tracers the structure of the gas boundary layer in the shock tube. By using these particles as tracers, velocity profiles of the boundary layer both in laminar and turbulent regions are measured and the velocity fluctuations observed. The time and space resolution of this technique is high. Laminar velocity profiles show a significant deviation from theoretical expectations. The turbulent average velocity profiles have the usual 1/7th power variation with distance from the wall in the top 90% of the layer. The velocity of the flow within a few microns from the wall is sometimes much greater than the value predicted by Mirels assuming zero velocity at the wall. A possibility of slip flow in the shock tube is discussed. This technique allows measurements to be made as close to the wall as the size of the particle's diffraction pattern, which is about 1 &mgr;.