Because inflation of a pyloric cuff during feeding blocks gastric emptying and increases gastric distention, this device was used to test the hypothesis of synergism between gastric distention and cholecystokinin octapeptide (CCK-8) in reducing intake. Adult, male Sprague-Dawley rat were allowed 20-min access to 30% sucrose, with or without inflation of pyloric cuffs, after intraperitoneal injection of saline or 1, 2, or 4 micrograms/kg CCK-8. Cuff inflation resulted in large increases in gastric volume at the end of feeding tests. However, this manipulation failed to enhance the effectiveness of any dose of CCK-8. In fact, data analyses revealed trends suggestive of decreased effectiveness of the two lowest doses under these conditions. The effect of 4 micrograms/kg CCK-8 was almost identical in tests with and without cuff inflation. These results are contrary to the prediction of greater potency of CCK-8 resulting from increased gastric distention.