Cerebral pan-angiography is the name we suggest for the visualization of all intracranial blood vessels, after injection of contrast medium in one of the carotid arteries. In 1957, in a preliminary report to this paper - read at the V Symposium Neuroradiologicum (First Congress of Neurologic Sciences - Brussels, Belgium) and published in Arquivos de Neuro-Psiquiatria (15:211-214, September, 1957) - we gave the theoretical bases of the method. Spontaneous filling of the vertebro-basilar system in a number of cases of carotid angiography suggested that a marked drop in blood tension and blood flow could be the responsible factor for the phenomenon. These circulatory changes might have their origin in a reflex elicited in a hypersensitive carotid sinus. Whatever the true mechanism of the arterial hypotension it was our feeling that deliberate cerebral pan-angiography might be accomplished by lowering the patient's blood pressure during the injection of the opaque substance. Ganglioplegic drugs failed to bring hypotension to desired levels: the effects of these drugs are not strictly proportional to the dosis in every case; there is interference of individual factors so that increasing the amount of hypotensive drugs might be dangerous in many cases. In order to avoid accidents this method was discarded. The blood stream blocking by means of intrathoracic hyperpressure, as described by Boerema and Blickman, seemed to be the method of choice for the task we had in mind. When the intrathoracic pressure reaches 50-60 mm. Hg. the blood tension falls to a very low level and pulsating of arteries disappears. Intracarotid injection of 15 ml. of 35% Nosylan soon after the arterial pulse is discontinued is proving quite satisfactory. Table 1 shows detailed data concerning the results we obtained in a series of 40 patients. In 38 patients out of this series intrathoracic hyperpressure lowered the cerebral blood circulation to such levels as to allow the contrast medium to flow into vessels not belonging to the territory of the injected artery, even against the normal blood stream. In the remainder two patients nothing but the branches of the injected carotid artery was contrast filled, despite the intrathoracic hyperpressure; we still do not know why intrathoracic hyperpressure failled to produce in these two cases the hemodynamic conditions required for contrast filling of blood vessels out of the field of the injected carotid artery. As soon as intrathoracic pressure is released the contrast medium leaves the arteries following the normal stream of cerebral circulation. We have not yet detailed data concerning the venous phase of pan-angiography. For such a purpose rapid serial equipment is required. Although this report is based on a small amount of cases we believe that cerebral pan-angiography is a harmless and safe method and it can be employed in every patient in which examination of both carotid fields and arteries of the vertebro-basilar system is required as, for instance, when intracranial aneurysms are suspected.