The complex mechanisms of action of androgens at multiple target organs have provided the groundwork for understanding the benefits and risks of testosterone therapy. A perception of male hormones as essential for male sexuality has now been greatly expanded to a broader understanding of the metabolic aspects of circulating androgens. The 3rd edition of this book on male hypogonadism provides a comprehensive yet focused view of testicular function and hormone related abnormalities involving the male reproductive system. It illustrates cutting edge knowledge on the diagnostics and therapeutic procedure for men with impaired testicular endocrine function. An extensive chapter deals with all aspects of androgen substitution therapy, including most recent and future developments. This book enables the practitioner to distinguish central from primary testicular causes of testosterone deficiency and provides a differential diagnostic approach to congenital and acquired forms of hypogonadism. It is ideally suited for the clinician in his strategic approach to the diagnosis and management of the androgen deficient patient.