Pelvic sonograms were performed every 2-3 days in 10 volunteers in order to study changes in thickness and texture that occur in the normal endometrium. A total of 75 sonograms were performed. The accuracy of sonographic estimates of endometrial thickness was also evaluated in eight patients who underwent hysterectomy for reasons unrelated to the uterus. The majority of sonographic measurements of endometrial thickness in these patients were within 1 mm of the actual thickness as measured in the unfixed specimen. In all of the individuals studied, sonography was able to depict changes in the thickness and texture of the endometrium which corresponded to the various phases of its development. Specifically, the average thicknesses of the endometrium were greater in the secretory phase (3.6 +/- 1.4 mm) than in the proliferative phase (2.9 +/- 1.0 mm) (p less than or equal to 0.05). The texture of the endometrium varied throughout the cycle with the hypoechoic texture slightly more common than echoic in the proliferative phase, whereas the echogenic appearance was most common in the secretory phase. Those technical factors which optimized sonographic depiction of the endometrium are discussed, as well as the possible clinical applications of the sonographic depiction of normal and abnormal endometria.