Ovarian volumes have been determined by pelvic ultrasonography in 2246 apparently healthy postmenopausal women of whom 2221 were included in the statistical analysis. Factors associated with gonadal size have been identified, and reference ranges for derived indices have been determined for use (in association with criteria for abnormal morphology) in a screening programme for ovarian carcinoma. The right ovary was present in 98.9% of subjects and the left in 99.1%. The mean (SD; range) of right and left ovarian volumes were 3.58 (1.40; 1.00-14.01) and 3.57 (1.37; 0.88-10.9) ml respectively. Significant predictors of ovarian volume were years since the menopause, weight, parity, age at menopause, a history of hormone replacement therapy, and previously diagnosed breast cancer. Abnormal ovarian volumes were assessed from a score equal to the (observed mean log volume (MLV) minus the predicted MLV)/0.327. A simplified nomogram has been prepared for routine clinical use. The relative abnormality of one ovary was assessed from a ratio score equal to loge (larger ovarian volume/smaller ovarian volume)/0.211 compared with the 99th centile for the Gaussian distribution.