Forearm cutaneous blood flow was monitored continuously by laser Doppler velocimetry in 12 normal human subjects before and after a 5-min topical challenge with 5 M propionaldehyde. The aldehyde challenge routinely provoked an increase in cutaneous blood flow. During the recovery phase from peak stimulated blood flow to a lower, stable, resting level of flow, the cutaneous blood flow exhibited rhythmic oscillatory activity. Three stages of oscillatory vasomotion were defined to characterize changes: the first 5 min after onset (I), the 5-min span bracketing the temporal midpoint (II), and the final 5 min (III). The average period, wave height, and erythrocyte flux decreased during these three stages of oscillatory vasomotion. These changes and the temporal characteristics of onset and disappearance of oscillatory vasomotion suggest an origin of the oscillations in the slow wave activity of vascular smooth muscle.