The present study assessed meal-contingent insulin effects on spontaneous meal patterns. Rats, trained to lever press for daily food requirements, showed stable meal patterns and were then implanted with hepatic-portal catheters. Once again stable in ingestion, animals received either physiological saline or vehicle plus 1 or 2 mU of regular, short-acting insulin beginning at 10 pellets into each initiated meal (which was the chosen minimum meal size definition). All meals during that day were then infused with the same solution and comparisons were made within animals (across days) only. Insulin reduced the size of spontaneous meals at both 1 mU (p < .01) and 2 mU doses (p < .001). No other meal parameters were significantly affected. In a complementary study, rats trained to lever press showed increases in meal size when "recovering from" a diazeoxide-adulterated diet (diazeoxide has been shown to limit insulin release). Thus, when insulin is increased during spontaneously taken meals, those meals are reduced in size and drugs which block insulin release, increase the size of meals; we assert insulin is a prandial satiety hormone which likely reduced feeding by increasing glucose uptake into peripheral tissue.