Subjects consumed soup (beef consomme) preloads of a fixed size containing different concentrations of monosodium L-glutamate (MSG). Effects on appetite following these preloads, and when no soup was consumed, were assessed in 3 studies. The soups supplemented with MSG were rated as more "pleasant," more "savoury" and more "satisfying" than soup with no added MSG. Compared with the no preload condition, consumption of the soups initially reduced appetitive motivational ratings and increased fullness ratings, but did not alter food intake in a test meal begun either 2 or 30 minutes later. This immediate inhibition of subjective motivation to eat was unaffected by MSG concentration. The failure of the soups to reduce subsequent food intake is presumably due to their low energy content (less than 10 kcal) and indicates that sensory stimulation alone is insufficient to reduce appetite. Indeed, the most important finding concerning MSG showed that motivation to eat recovered more rapidly following a lunchtime meal in which MSG-supplemented soup was served as the first course (compared both with the effect of unsupplemented soup and no preload). It is suggested tentatively that MSG through its stimulation of orosensory receptors and/or by improving the palatability of the soup may have influenced the metabolic disposal of nutrients consumed in the previous meal.