Previous studies have demonstrated expression of insulin-like growth factor-binding protein (IGF BP-1) in secretory and decidualized endometrium, in adult and fetal liver, and in HepG2 liver cancer cells. We have studied the expression of IGF BP-1 in various types of ovarian neoplasias, normal ovary, and granulosa cells from hyperstimulated human ovarian follicles by RNA blot hybridization. A single 1.6 kb mRNA species, similar to that present in human decidua, was identified in poly(A)RNA-containing preparations of granulosa cells and of a borderline malignant ovarian cystadenoma. This finding verifies the postulated production of IGF BP-1 by the human ovary.