Forearm cutaneous blood flow was monitored continuously by laser Doppler velocimetry in 10 normal human subjects before, during, and after external brachial artery occlusion for 6 min duration. During the reactive hyperemic response, the cutaneous blood flow exhibited rhythmic oscillatory activity. The amplitude of the oscillations was maximum 30 s postocclusion. Thereafter, the amplitude of the oscillations declined until cutaneous blood flow returned to control values. The mean (+/- SEM) period for the oscillations was 9.26 +/- 0.30 s. Bilateral forearm sites were examined simultaneously in eight studies and demonstrated a progressive loss of synchronicity. Nine additional studies were performed in which two forearm sites only 1.8 cm apart demonstrated a progressive loss of synchronicity resulting from different periodicities of microcirculatory flow patterns. These oscillations in cutaneous blood flow, which occur during postocclusive reactive hyperemia as a normal physiological phenomenon, are not synchronous in adjacent areas of skin. The data suggest an origin of the oscillations in the cutaneous vasculature that is either unrelated to sympathetic vasoconstrictor influences or is due to nonuniform cutaneous sympathetic excitation.