We have established an in vivo experimental model in which human ovarian cancer grows in the ovary of nude mice and metastasizes to parenchymatous organs. An ovarian cancer cell line was orthotopically injected into the nude mouse ovary together with Matrigel by microsurgical techniques. The cells grew locally in the ovary and metastasized to the peritoneum, colon, omentum, liver, and spleen. When the cells were injected into the intraperitoneal cavity with Matrigel, they formed carcinomatous peritonitis but neither ovarian tumor formation nor the metastasis to parenchymatous organs was detected. Taken together, these findings indicate that the microenvironment of the ovary seems to be essential for metastasis of implanted human ovarian cancer cells. This in vivo experimental model allows us to investigate the mechanism of the metastasis of ovarian cancer, it will be also useful for the establishing a new therapeutic approach to preventing metastasis of human ovarian cancer to parenchymatous organs.