A new embolus consisting of a fibrin clot containing an anticancer drug (mitomycin-C) was devised. An experimental study was then performed using the new embolus in dogs and several interesting characteristics were observed. The fibrin clot containing mitomycin-C was in a fluid from when infused and its action as an embolus did not occur until it reached a target artery. The fibrin clot containing mitomycin-C formed a mold within of the arteries in which it was embolized and was soluble with urokinase during a ten-hour period. The release of mitomycin-C from the fibrin clot was sustained over sixty hours. The intraarterial occlusion formed by fibrin clot was temporary, and recanalization was observed over forty-eight by hours by both angiography and pathological examination.