In order to study the contrast filling of arteries which are not part of the injected vessel territory, a series of 700 carotid-angiographies performed in the "Hospital das Clínicas de São Paulo" is reviewed. The post-communicating segment (see fig. 3) of the ipsilateral posterior cerebral artery was filled in 42.5% of the cases. The post-communicating segment of the contralateral anterior cerebral artery was found in 49.4%; the contralateral sylvian artery as well as the corresponding pre-communicating portion of the anterior cerebral artery was filled in 4.85% of the cases; the pre-communicating segment of the contralateral anterior cerebral alone was seen in 9.85%). The incidence of contrast filling of other arteries which do not belong to the vascular bed of the injected artery can be seen in table 1. In 19 instances out of the 700 angiographies reviewed, the contrast medium filled the basilar artery and its main branches. Three similar cases, from the private clinic, are included in this report on account of their peculiar aspects. Carotid-angiographies in which the basilar artery is filled have been reported as being very unusual; Torkildsen fount just one case in a series of 2,800 carotid-angiographies. The authors emphazise the value of the systemic blood pressure in the mechanism of contrast filling of the basilar; according to them a severe drop in systemic blood pressure is an essential point. This hypotension being transient and rapidly reversible may be related to a hyperactive carotid sinus reflex. Although it represents merely an hypothesis, the authors think it envolves a very practical interest; once it was proved, the visualization of the entire intracranial arterial field could be achieved by injecting the contrast medium in a carotid artery, under induced and controlled blood hypotension.