It has been reported that newly developed nonionic contrast material is less effective in anticoagulation than ionic contrast media. Anticoagulation properties were studied with high osmolar ionic contrast medium(diatrizoate) low osmolar ionic medium(ioxaglate) and low osmolar nonionic contrast medium(iopromide) as well as with normal saline for control Arterial blood was taken from 10 adults before angiography. Two ml. of the arterial blood was introduced into the plastic syringes containing 2 cc. of each contrast medium and saline. The syringes were kept undisturbed in room temperature for 10 minutes 30 minutes 60 minutes 90 minutes and then the blood-contrast mixture was poured on the filter paper to detect the clots formed in the syringes. Delay of the clotting time was also checked in the contrast media with various concentraions of 100% 30% 10% and 3% Chi-square test of the data shows very significant difference in antico-agulation effect between the ionic group(diatrizoate ioxag-late) and the nonionic one (iopromide) Clotting time in the nonionic medium(iopromide) was shorter in 30% concentration than that of the ionic material(diatrizoate ioxaglate) Nonionic contrast medium(iopromide) has anticoagulation effect but less effective than ionic media(diat-rizoate ioxaglate).