The present study compared the effects of a high- and normal-casein-protein breakfast on satiety, 'satiety' hormones, plasma amino acid responses and subsequent energy intake. Twenty-five healthy subjects (BMI 23.9 (SEM 0.3) kg/m2; age 22 (SEM 1) years) received a subject-specific standardised breakfast (20% of daily energy requirements): a custard with casein as the single protein source with either 10, 55 and 35 (normal-casein breakfast) or 25, 55 and 20 (high-casein breakfast) % of energy (En%) from protein, carbohydrate and fat respectively in a randomised, single-blind design. Appetite profile (visual analogue scale; VAS), plasma glucose, insulin, glucagon-like peptide 1, ghrelin and amino acid concentrations were determined for 4 h; here the sensitive moment in time for lunch was determined. Subjects came for a second set of experiments and received the same custards for breakfast, and an ad libitum lunch was offered at 180 min after breakfast; energy intake was assessed. There were increased scores of fullness and satiety after the 25 En% casein-custard compared with the 10 En% casein-custard, particularly at 180 min (26 (SEM 4) v. 11 (SEM 5) mm VAS; P<0.01) and 240 min (13 (SEM 5) v. -1 (SEM 5) mm VAS; P<0.01). This coincided with prolonged elevated plasma amino acid concentrations; total amino acids and branched-chain amino acids were higher after the 25 En% casein-custard compared with the 10 En% casein-custard at 180 and 240 min (P<0.001). There was no difference in energy intake (3080 (SEM 229) v. 3133 (SEM 226) kJ for 25 En% and 10 En% respectively; NS) from the ad libitum lunch. In conclusion, a breakfast with 25% of energy from casein is rated as being more satiating than a breakfast with 10% of energy from casein at 3 and 4 h after breakfast, coinciding with prolonged elevated concentrations of plasma amino acids, but does not reduce subsequent energy intake.