This work describes an instrument for the noninvasive measurement of cutaneous blood flow velocity. The system utilizes the Doppler shift of laser light backscattered from moving red blood cells in the cutaneous microcirculation, the shift being obtained by an optical heterodyning technique. Comparison is made between this technique and the 133xenon clearance technique in measuring cutaneous flow in the forearms of normal volunteers. Variations in flow were obtained by inducing different degrees of solar erythema with an ultraviolet sunlamp. A Y on X linear regression yielded a regression coefficient = 0.89 (p less than 0.001, n = 16) between the two methods. The laser Doppler method appear to represent a practical technique for clinical evaluation of cutaneous blood flow in any skin surface.