James Fitzsimons's experimental demonstration of the important involvement of the renin-angiotensin system in the control of thirst and sodium appetite is a landmark in our understanding of the physiological basis of thirst. He has found that angiotensin II acts both peripherally and in the brain to stimulate fluid and electrolyte intake. Studies on the central actions of renin and angiotensin have defined probable hypothalamic targets for these effects and suggested the involvement of an intrinsic renin-angiotensin generating system in brain. His work helps to illuminate the functional organisation of the hypothalamus and vegetative functions in general, and suggests the possible physical basis of a motivational state. He received a Docteur honoris causa en Médecine de l'Université de Lausanne, Suisse in 1978, and the Distinguished Career Award of the Society for the Study of Ingestive Behavior in 1998.