THIS STUDY compares the effects of meglumine iothalamate 60 per cent (60 per cent Conray, Mallinckrodt) and 50 per cent sodium diatrizoate (50 per cent Hypaque, Winthrop) on arterial blood pressure during and after angiography. In a previous report, we noted briefly the observation of a difference in blood pressure changes following the intra-arterial administrations of meglumine iothalamate 60 per cent as compared to 50 per cent sodium diatrizoate in a limited number of cases (2). This investigation was carried out to study these differences more thoroughly. Material and Methods A total of 50 intra-arterial blood pressure measurements were made in 24 patients examined for cerebrovascular disease. The group was comprised of 19 males and 5 females, with an age range of forty to sixty-five years. Percutaneous retrograde brachial angiography was carried out in every case. Two 16-gauge Cournand needles were placed in the same brachial artery; the lower for the injection of contrast medium and the upper, 10 to 12 em more proximal, for blood-pressure recording. Injections were made with an automatic injector (Taveras, Picker) set at a pressure of 625 lb. per square inch. Intra-arterial pressures were measured with a Statham P23AC pressure transducer and recorded on a Grass model 5 polygraph. The detailed technics of injection and blood-pressure recording were described previously (2). The volume of contrast medium was 40 cc for each injection. The patients were divided into three groups. Six received only meglumine iothalamate 60 per cent. In a second group of 16 patients meglumine iothalamate 60 per cent was followed after an interval of thirty minutes by an injection of 50 per cent sodium diatrizoate. Six patients received 50 per cent sodium diatrizoate followed after an interval of thirty minutes by an injection of meglumine iothalamate 60 per cent. Four of these patients were included in Group 2 at another angiographic session. Results In all cases the blood pressure rose initially. This elevation of pressure, it has been demonstrated, is proportional to injection pressure and bolus size independent of the material injected (2). In Group I, three to four seconds after the injection of meglumine iothalamate, 60 per cent, there was a slight fall of blood pressure from 10 to 25 mm Hg. This lasted three to sixty seconds and was followed by a return to preinjection levels (Fig. 1). In Group II, there was a blood pressure depression from 10 to 25 mm Hg for three to fifty seconds following the injection of meglumine iothalamate 60 per cent. After the injection of 50 per cent sodium diatrizoate the drop was more profound, ranging from 10 to 75 mm Hg for three to sixty-eight seconds (Fig. 2). In Group III, there was a 10 to 50 mm Hg fall of blood pressure lasting twelve to sixty seconds after the injection of 50 per cent sodium diatrizoate.