A daily longitudinal study enduring for more than two years was made of an ambulance patient whose mood changed predictably every 35 days from a profound retarded depression through euthymia up to hypomania and back to depression. The patient employed a self-reporting bipolar mood scale for this study. Weekly hour-long recordings of aspects of her vascular system were made of her electrocardiography, arterial pressures and electrical impedance plethysmography. Correlations were sought between mood scores and these physiological changes. Time series analysis of her auto-cross-correlograms indicated that the vascular elements preceded the mood change in a predictable sequence. Heart rate and percent rise time had the shortest cycles and were the earliest indices of change; amplitude and inflow angle, the next; while arterial pressures were the slowest. The genesis of mood change as an impedance function of the relationship of neurotransmitter to cerebral microvasculature is discussed.