Two studies were designed to compare the effects on post-ingestive satiety of manipulating the degree of saturation of fatty acids, at a fixed chain length (18 C atoms), in a fixed energy (5·68 MJ for males; 3·97 MJ for females), high-fat (55 % energy) lunch meal. Two different groups of twenty subjects (ten males and ten females) took part in each study. All forty subjects were of normal weight and aged between 18 and 36 years. Study 1 compared the effects of fat A (oleic blend, high in monounsaturated fatty acids (MUFA)) with those of fat B (linoleic blend, high in polyunsaturated fatty acids (PUFA)) and fat C (stearic–oleic blend, high in saturated fatty acids (SFA)). Study 2, which was designed to confirm and extend the findings of Study 1, compared the effects of fats A, B and C with those of fat D (a linoleic–oleic blend). Energy and nutrient intakes were monitored for the rest of the day and for the following day. Profiles of hunger, fullness and other sensations were monitored by continuous tracking and end-of-day questionnaires. In each meal the fat content was exclusively composed of one particular type (A, B, C or D) and was divided equally between the main course and dessert. Study 1 revealed a significant effect of fat type (degree of saturation) on intake of nutrients at the following (dinner) meal (smallest F[2,36] 3·38, P < 0·05), on post-ingestive ratings of motivation to eat (smallest F[2,36] 4·18, P = 0·02) and on energy intake over the whole test day (F[2,36] 3·39, P < 0·01). Subjects consumed significantly more energy after consumption of the lunch containing fat A than after the lunches containing fats B or C and there was a trend for these effects to continue into the second day. In Study 2, fat C produced more similar effects on appetite to fat A and there was a tendency for subjects to consume more over the whole test day when they had consumed the lunch containing fat A than when they had consumed the lunch containing fat B. Furthermore, when the data from fat conditions A and B in both studies were combined (n 40) the results of Study 1 were confirmed. Overall, the results of these short-term studies indicate that PUFA may exert a relatively stronger control over appetite than MUFA and SFA.