The experiments reported here were designed to investigate the role of the duodenum in conjunction with the palatability of the diet in the control of meal size. Rats fitted with chronic cannula resting in the duodenal cap were infused with 15 ml of 5.05% glucose, 10.1% glucose, 1.6% urea, 3.2% urea, 15.15% glucose and 4.8% urea at a rate of 0.2 ml/min, or were not infused at all. In one experiment, intake of sweetened condensed milk, and in a second experiment, intake of a 3.2% glucose solution was recorded over a 5 1 2 hour period. Only infusions of very concentrated solutions had significant effects on milk ingestion. On the other hand glucose infusions isosmotic to body fluids led to a decrease in the size of the first meal of a 3.2% glucose solution and a lengthening of the subsequent intermeal interval. These effects were directly related to the concentration of the glucose infused. Equiosmolar urea infusions had no consistent effect on glucose drinking. Intake of moderately palatable substances can be altered by the presence of small amounts of glucose in the duodenum, but intake of highly palatable substances remains largely unaffected unless high concentrations of glucose are infused.