From the intraarterial infusion tube in the proper hepatic artery, 5-10 mCi of 133Xe (T1/2 = 5.3 days) was injected. The duration of blood stagnation (T1/2) in the tumor site was obtained from the washout curves in the tumor site and the nontumor site as the duration from the peak to the decrease to half value. The results indicated that the stagnation lasted 110.3 +/- 70.0 seconds in the tumor site, and 80.1 +/- 41.0 seconds in the non-tumor site, showing that the blood was more apt to be stagnant in the tumor site than in the non-tumor site. In the foci in which the stagnation in the tumor site (T1/2) was more than 100 seconds, the response was obtained for 6 (75%) out of 8 foci, which was higher than 3 (60%) out of 5 foci having abundant vascularity. In the foci in which the stagnation in the tumor site did not exceed 80 seconds, no response was obtained irrespective of the vascularity. From the above review, the intraarterial infusion method for the metastases of colorectal cancer was effective for the case which required a long time for washout of the anticancer agent at the tumor site.