This study investigated the hypothesis that the smaller the particle size of the food, the higher the glycaemic-insulin response and the lower the satiety rating.Ten healthy subjects consumed equal carbohydrate portions of four test meals of equivalent nutritional composition based on four different grades of wheat: whole grains, cracked grains, coarse and fine wholemeal flour.The mean overall plasma glucose response (area under the curve: AUC) was highest for the fine flour meal (4205 +/- 451 mmol/l.120 min), followed by the coarse flour and cracked grain meals and lowest for the whole grain meal (1524 +/- 190 mmol/l.120 min). Insulin responses showed the same ranking but satiety responses were the reverse, the fine flour meal giving the lowest satiety response [AUC: 231.4 +/- 31.6 rating scale (RS) units.120 min] and the whole grain meal the highest response (AUC: 318.4 +/- 29.3 RS units.120 min). Total insulin responses (AUC) were significantly associated with subjective satiety when analyses on an individual basis (analysis of covariance coefficient = -0.024, P < 0.04) such that for every 1000 unit increase in AUC insulin, satiety decreased by 24 units (13% on average).The results suggest that the processing of cereals is not only a major determinant of the glycaemic and insulin response but also affects the levels of postprandial satiety.