The specific retention of androgens and oestrogens by cytoplasmic components of human ovarian tumours was investigated. High-affinity, low-capacity binding of androgens was observed in 88% of tumour specimens and oestrogen binding in 32%. Retention of oestrogens did not occur in the absence of androgen binding. The androgen-binding component, of sedimentation coefficient 7·5–8·5S, showed specificity for 5α-dihydrotestosterone and 17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one (R1881). In some instances, competition for R1881-binding sites indicated the presence of progesterone receptor-like binding. The data presented suggest strongly the existence of androgen and oestrogen receptors in some ovarian tumours and may be relevant to histopathological classification and therapeutic rationales.