Animal studies suggest that the effects of fatty acids on gastric emptying and pancreatic secretion are both concentration and load dependent, while their suppressive effect on energy intake is only load dependent. We postulated that, in humans, the modulation of antropyloroduodenal pressure waves, plasma cholecystokinin (CCK) and peptide YY (PYY) concentrations and energy intake by intraduodenal lauric acid, a fatty acid with 12 carbon atoms ('C12') would be load, but not concentration, dependent. Two groups of 12 healthy males were each studied on three separate occasions in double-blind randomized fashion. Antropyloroduodenal pressure waves, plasma CCK and PYY, and appetite perceptions were measured during intraduodenal infusions of C12 at (1) different loads of (i) 0.2, (ii) 0.3 and (iii) 0.4 kcal min(-1) (all 56 mM) for 90 min, and (2) different concentrations of (i) 40, (ii) 56 and (iii) 72 mM (all 0.4 kcal min(-1)) for 60 min. Energy intake at a buffet meal consumed immediately following each infusion was quantified. Suppression of antral and duodenal pressure waves, stimulation of pyloric pressure waves, stimulation of plasma CCK and PYY, and suppression of energy intake, were related to the load of C12 administered (r>0.65, P<0.05). In contrast, there were no concentration-dependent effects of C12 on any of these parameters. In conclusion, in humans, the effects of intraduodenal C12 on antropyloroduodenal motility, plasma CCK and PYY and energy intake appear to be related to load, but not concentration, at least at the loads and concentrations evaluated.