An immunoperoxidase technique has been utilised for the demonstration of follicle stimulating hormone (FSH), luteinising hormone (LH) and prolactin (PRL) binding sites in normal human ovaries and in a wide range of benign and malignant epithelial tumours of the ovary. The incidence of FSH, LH and PRL binding was, respectively, 32%, 41% and 39% in normal ovaries, 30%, 18.5% and 22.5% in benign e...