The temporal and quantitative relationship between food and water intake and the effect of fluid restriction on voluntary food intake were studied in 20 male subjects over two 48-h periods. Food intake was limited to specific mealtimes, but subjects could eat as much as they wanted during these times. Drinking was ad libitum in one condition, and limited by about 40% of ad libitum drinking in the other condition. Approximately 68% of all drinking occurred when food was available at mealtimes when drinking was ad libitum. When fluid intake was limited, subjects voluntarily reduced their food intake. Food acceptability, as measured by hedonic ratings, was not significantly affected by fluid restriction even though food intake was significantly reduced. The intensity rating of thirst was negatively correlated with food intake. Indirect comparisons are drawn with eating and drinking relationships in non-human species.