Estrogen and progesterone receptors were measured in cystosols prepared from 32 normal ovaries and 25 benign and 49 malignant ovarian tumors. In normal ovarian tissue, estrogen and progesterone receptors were detected in 22 and 75% of specimens, respectively. Estrogen receptors were present in low concentrations ranging from 2 to 9 fmol/mg cytosol protein. The estrogen receptor content and distribution were similar in benign tumors (20%), but progesterone receptors were significantly decreased in 16% of specimens (P less than 0.001). In malignant ovarian tissues, estrogen receptors were present in 57% of specimens in concentration ranging from 1 to 132 fmol/mg cytosol protein. Of these, 72% of tissues had estrogen-receptor concentrations greater than 10 fmol/mg cytosol protein. The presence of estrogen receptors in ovarian cancer was significantly different from normal ovaries and benign tumor tissues (P less than 0.01). Progesterone receptors were detectable in 29% of ovarian cancer specimens. Estrogen and progesterone receptors were present alone or in combination, in 65% of ovarian cancers. The similarity in sex steroid content between ovarian and breast cancer warrants prospective studies of sex steroid receptor content in ovarian malignancies as a possible predictive index of survival and response to hormone therapy.