Jeffrey Friedman is interested in the molecular mechanisms that regulate food intake and body weight. Genetic studies in mice led him to identify leptin, a hormone made by fat tissue that plays a key role in controlling appetite and weight. Now Friedman and his team are working to understand how leptin mediates these functions. They are also seeking to identify other key regulators of body weight. Their work has practical implications for health issues related to nutritional state, including obesity, diabetes, and certain female reproductive disorders.