Uterine factors contributing to infertility include abnormalities in the myometrium and in the endometrium. Recent studies have mainly addressed endometrial factors. Several methods have been developed to evaluate endometrial function, including quantitative histology, electron microscopy, histochemistry and immunohistochemistry, hysteroscopy, measurement of endometrial protein levels in plasma or endometrial washings, and ultrasonography. The relationship between endometrial abnormality and types of infertility has been explored by various investigators, as has endometrial receptivity in women over 40 years of age, with interesting results. Unfortunately, the best treatment for endometrial defect is still unknown. A better understanding of the precise nature of the abnormality should lead to effective treatment.