Previous studies have demonstrated locally increased steroid production and release of EGF/TGF-alpha in ovarian carcinomas. The influence of added steroid hormones on EGF-like activity in ovarian tumours in vitro was investigated. Using radioreceptor assay, EGF-like activity was measured in media from incubations of postmenopausal ovaries, benign and malignant epithelial ovarian tumours from 27 patients. The 3-hour incubations were performed with and without addition of progesterone, testosterone or estradiol. Addition of progesterone and estradiol significantly increased the release of EGF/TGF-a from benign tumour tissue but did not stimulate release from control ovaries. A stimulating effect was also noted for malignant tumour tissue but the increase was not significant. Addition of EGF or IGF-1 did not affect the release of steroid hormones from ovarian tumours. A positive correlation between progesterone and EGF-like activity was found in incubation media of peritoneal fluid cells from cancer patients.