This study compared the effects of high- and low-energy lunches upon subjective motivation to eat and food intake. Subjects ate four cooked lunch-time meals on separate days, two of which were high-energy (1820 kJ or 435 kcal) and two low-energy (1090 kJ or 260 kcal). The meals were of similar bulk, contained similar amounts of protein and carbohydrate but different fat contents, the low-energy meals containing very little. Motivational ratings and food preference assessments were completed before, and at hourly intervals for 3 h after the meals during which time subjects were not allowed to eat. Food intake diary records were kept for the rest of the day. Immediately after consumption of the meals none of the ratings differentiated between the high- and low-energy meals. At 1 h rated hunger was significantly higher after the low-energy meal and by 3h high- and low-energy meals were significantly differentiated by almost all measures. When subjects were allowed to eat freely, food intake records showed that energy intake was higher following the low-energy meal during the first 2 h but was lower thereafter. At the end of the assessment period (i.e. 8h after lunch) subjects had made a statistically non-significant 43 per cent compensation for the energy 'lost' at lunch. These findings are of theoretical importance since they provide evidence of short-term monitoring of energy. This study is of practical significance since it discloses certain consequences of using reduced energy foods which may form part of a weight control programme.