for a better understanding of the complex mechanism of the menstrual cycle, and sheds some light on its pathophysiology. Such an approach adds ariother dimension to interpretation of many menstrual abnormalities and numerous aspects of infertility in women with normal physiognomies and apparently regular menstrual cycles. The pathologist must be aware of these new concepts since a knowledge of functional changes reflected in hormone serum levels and sex steroid receptor concentrations allows a mare detailed analysis and a better interpretation of the structural features of the endometrium. This information placed in the proper clinical context can help the gynecologist provide optimal therapy. The reader will find a valuable reference for a synthesis of clinical, morphological, and biochemical data related to the menstrual cycle and its aberrations.