Human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) are placental proteins whose ectopic secretion by non-trophoblast tumours has been claimed to be of clinical relevance. Radioimmunoassays for hCG and hPL, together with human luteinising hormone (hLH), have been established and plasma levels were measured in 61 patients with carcinoma of the ovary. Approximately 51% of the patients were found to have raised plasma hCG levels. Such raised titres were not stage or tumour-type related but occurred only in post-menopausal subjects. The majority of patients with raised hCG levels also had raised plasma hLH levels. Assay cross-reactivity was shown to account for the 'spurious' hCG elevations. However, hCG may be an ectopic product in a minority of tumours; elevated plasma hCG levels were shown to coexist with low hLH levels. Although such lesions did not show morphologically identifiable choriocarcinomatous elements, all were poorly differentiated carcinomas. In some cells hCG was demonstrated by immunocytochemical methods. No patients had a raised plasma hPL level. It is concluded that these placental proteins are of no clinical use in the management of ovarian carcinoma patients.