Sodium vapor seeded into a hypersonic helium flow through an orifice on a model is used as a tracer to determine velocity profiles. A narrow‐linewidth tunable dye laser is scanned across the Doppler‐shifted absorption line of the sodium and the resonant fluorescence is observed. Curves showing the velocity‐shifted pressure‐ and temperature‐broadened absorption lines at several points in the flow are presented. Fluorescence is strong enough to use this technique for quantitative flow visualization: at each laser frequency, a specific velocity component is highlighted and easily observed by eye.