Twenty-eight cervicovaginal tracts from approximately 2-year-old female BALB/cCrgl mice neonatally exposed to ovarian steroids were cut into small segments and transplanted into syngeneic hosts. Within six months, six of 28 host animals developed tumors. Three tumors were from progesterone-exposed mice, two were from estrogen-exposed mice, and one was from estrogen-progesterone-exposed mice. These tumors have been maintained by serial transplantation for approximately two years. The progesterone-induced tumors are mixed tumors with both squamous cell and glandular components. The estrogen-induced tumors are squamous cell carcinomas. The estrogen-progesterone-induced tumor was originally a squamous cell carcinoma, which now resembles a basal cell carcinoma. The other tumors have maintained their original morphological characteristics. All tumors have proven to be hormone independent. No control cervicovaginal tracts developed tumors after transplantation, even after 24 months in the host animals.