In a rabbit tongue cancer model, prepared by transplantation of VX2 carcinoma, the dynamics of fibronectin (FN) with the passage of times was investigated in two groups: an untreated group with active tumor proliferation a group in which tumor proliferation was suppressed by anticancer treatment. The response of FN surrounding the transplanted tumor was strongly positive reaction on day 7 after transplantation in contrast, strongly positive reaction tended to persist when tumor proliferation was suppressed. Cervical lymph node metastases were observed about the time when the FN response surrounding the transplanted tumor decreased. Furthermore, the cellular FN (cFN) response (Extra Domain A; ED-A expression) was negative reaction on day 7 after transplantation, and was thereafter expressed gradually. The expression in the group with suppressed tumor proliferation was greater than that in the group with active tumor proliferation. The FN/cFN response at metastasized lymph nodes were observed only in small case of cancer tissue wihch appeared to represent initial metastasis formation; all sites showing FN response also showed cFN response. Increased FN concentration in blood is not due to tumor bearing status, and it doesint increase until tumor proliferation is active, and it's measurement with the passage of times can therefore serve as a parameter of tumor proliferation activity. FN concentration in blood which increased during tumor proliferation was attributed to increase in either intact plasma FN (pFN) or ED-A free FN fragment by western blotting analysis of FN in plasma. For FN, there was no relation between the response surrounding the tumor and the blood concentration. The cFN response surrounding the tumor was therefore considered to be one of cancerous stroma reactions that had an inhibitory effect on the cancer. It was suggested that monitoring FN, especially cFN response surrounding the tumor, can serve as a useful parameter for evaluating treatment regimens and prognoses.