It has been reported that newly developed nonionic contrast material is less effective in anticoagulation thanionic contrast media. Anticoagulation properties were studied with high osmolar ionic contrastmedium(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 thearterial blood was introduced into the plastic syringes containing 2cc. 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 theclotting time was also checked in the contrast media with various concentrations of 100%, 30%, 10%, and 3%.Chi-squre test of the data shows very significant difference in antico-agulation effect between the ionicgroup(diatrizoate, ioxaglate) and teh nonionic one(iopromide). Clotting time in the nonionic medium(iopromide) wasshorter in 30% concentration than that of the ionic material(diatrizoate, ioxaglate). Nonionic contrastmedium(iopromide) has anticoagulation effect, but less effective than ionic media(diatrizoate, ioxaglate).