Sequential gray-scale sonograms were obtained during 20 menstrual cycles in 16 normal female volunteers. Hormonal and physical parameters of an ovulatory cycle were correlated with morphological changes in the ovaries, uterus, and cul-de-sac as seen on the sonogram. Ovarian cysts of two sizes were observed, corresponding chronologically and morphologically to Graafian follicles and corpora lutea. Small amounts of free pelvic fluid were demonstrated in many women at ovulation. A characteristic uterine appearance is seen prior to menstruation and is related to hormonal influences on the uterus. These findings emphasize the importance of recognizing normal physiological changes when interpreting gynecologic sonograms.