Plasma secretin levels were measured during a 72-hour starvation period in dogs. Plasma secretin rose significantly and insulin levels fell significantly during starvation. Intravenous glucose loading at the end of the 72-hour starvation period suppressed plasma secretin and free fatty acid levels with a concomitant rise of glucose and insulin levels. These findings suggest that secretin might be regulated by plasma glucose and insulin levels and might play a role in lipolysis during starvation.