Rabbits were injected with 1-2 ml autologous blood into the chiasmatic and basal cisterns to stimulate subarachnoid hemorrhage. Selective vertebral angiography performed at various time-periods following blood injection showed a 27 per cent reduction in basilar artery diameter within 3-5 days, followed by normalization so that pre-injection size was regained within 26 days after the treatment. Formaldehyde histofluorescence of the major basal pial arteries showed almost 75 per cent reduction in number and fluorescence intensity of visible perivascular adrenergic nerves at 3-7 days following blood injection. The noradrenaline fluorescence in a normal number of nerves returned to control values at 26 days after treatment. The noradrenaline reduction in the perivascular nerves was confirmed in fluorometric determinations. The presence of cisternal blood markedly impaired the neuronal uptake of 3H-noradrenaline at 3 days following the injection. The transmitter uptake had normalized 2 weeks later. The impaired neuronal uptake of noradrenaline in the presence of cisternal blood is in accordance with the net reduction in transmitter of the perivascular nerves, and may provide one pathophysiological factor in the development of angiographically visible vasoconstriction, having a time-course resembling that of the functional changes in the perivascular adrenergic nerves.