A piece of gelatin sponge was inoculated submesothelialy in the abdominal wall of female Donryu rats, and 1, 2, 4, 7, 14, or 21 days later, 1 x 10(5) cells of ascites hepatoma AH39 were intraperitoneally transplanted. Tumor cells were detected in the area of gelatin sponge inoculation in each group 2 to 5 days after the transplantation. Generally, the number of rats in which tumor cells were detected was larger in those transplanted with tumor cells within a short period after the gelatin sponge inoculation. Changes in the area of gelatin sponge inoculation and nontreated area in the rats which received intraperitoneal transplantation of the tumor cells on the 1st day after gelatin sponge inoculation were studied. Tumor cells were detected in the area of gelatin sponge inoculation as early as 2 days after the tumor transplantation, whereas they were detected on the 14th day in nontreated areas. Tumor detection was preceded by inflammatory reaction in both cases.