An analysis of abnormalities of the retinoblastoma gene in human ovarian and endometrial carcinoma. The altered expression of the human retinoblastoma (RB) gene has been demonstrated to play an important role in the pathogenesis of RB and other tumors. To determine whether the RB gene might be involved in the pathogenesis of human ovarian and endometrial cancer, DNA from 24 human ovarian tumors, 3 normal ovaries, 3 endometrial carcinomas, and 1 endometrial hyperplasia was examined with an RB complementary DNA probe. Evidence for homozygous deletion of the RB gene was observed in only one specimen. Interestingly, the specimen was an endometrioid tumor of the ovary of low malignant potential (LMP). This patient experienced rapid progression of the tumor and died 8 months after diagnosis. Abnormalities of the RB gene may be involved in the aggressive biologic behavior of certain forms of ovarian carcinoma, particularly those of LMP. 