Recent advances in cellular and molecular biology have markedly increased our understanding of normal and abnormal hypothalamic-pituitary-testicular function. Like other volumes in the Contemporary Endocrinology series, the goal of Male Hy- gonadism: Basic, Clinical, and Therapeutic Principles is to link current knowledge of basic biology to the practice of medicine. The development of new methods for testost- one replacement has substantially increased the number of men who are seeking to determine whether they are hypogonadal, and who are using testosterone replacement therapy, thus...