Cultured bovine granulosa cells express the gene encoding basic fibroblast growth factor (bFGF). The bFGF gene is transcribed into 7.0- and 3.7-kilobase mRNA transcripts which are apparently translated into 16,000 mol wt bFGF-like growth factor. The granulosa cell-derived bFGF is bioactive, i.e. it can stimulate the proliferation of capillary endothelial or granulosa cells. This mitogenic effect is prevented by specific neutralizing anti-bFGF antibodies. Our results indicate that bFGF derived from granulosa cells can act as both autocrine and paracrine growth factor, and they further suggest that the factor may be involved in the development of the rich vasculature of the theca interna of the follicle.