The estrogen-producing activity was investigated in subjects with common epithelial tumors and dermoid cysts, which were not included in the category of hormone-producing tumors. Serum estradiol (E2) in peripheral blood of patients with ovarian tumors were assayed pre-and post-operatively. In addition, cytological examinations of vaginal smears and histological examinations of the endometrium were carried out. The results were as follows: The mean of preoperative serum E2 levels in postmenopausal cases (16) was 230.9 +/- 248.5pg/ml, which was significantly higher than the control of the same age group (p less than 0.01). In seven (63.3%) out of 11 cases followed up, a distinct postoperative decline was indicated in the serum E2 level. The mean of preoperative serum E2 levels in 28 cases of premenopause collected in the early follicle phase was 135.6 +/- 148.8pg/ml, which was apparently higher than the level in normal females in the follicle phase. Also, an evident decline was observed postoperatively in the E2 level in 8 (40%) out of 20 cases. The cytological observations of vaginal smears in 44 cases of postmenopausal ovarian tumor provided the following results: The karyopyknotic index was 12-23% on the average in each age group, which was comparatively higher than that of the control. The maturation index also indicated a deviation to the right compared to the control. The following were the results of histological examinations of the endometrium carried out in 23 cases of postmenopausal ovarian tumor: 5 cases (21.7%) of proliferative endometrium; 3 cases (13.0%) of cystic hyperplasia and 2 cases (8.7%) of adenomatous hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)