This case is designed to help students develop a deeper understanding of negative feedback regulation. Basic principles of negative feedback systems are illustrated by focusing on the effects of anabolic steroids on the hypothalamic-pituitary-testicular system. The use of these drugs in sports provides the context for the case. Specifically, the case provides basic information about the regulation of testicular function and then focuses on a side effect of anabolic steroid use; i.e., testicular atrophy. Students are required to develop hypotheses to explain this side effect and devise ways to test their hypotheses. They are also asked to think beyond the scope of the case and apply basic principles to explain other conditions affecting testicular function. The case is suitable for use in any physiology course and might also be useful for a core course in general biology.