Acquisition performance of rats in a simple runway was investigated as a function of percentage reinforced trials (100% vs. 50%) and injection solution received prior to daily training (sodium amytal vs. isotonic saline) in a 2 X 2 factorial design. The results obtained from 4 groups of 12 Ss showed 50% reinforcement to lead to faster final speeds than 100% reinforcement with saline control injections; whereas this order was reversed under training with sodium amytal. The results were predicted from a frustration theory interpretation of random partial reinforcement and the assumption that anticipatory frustration is particularly suspectible to the depressant action of sodium amytal. (PsycINFO Database Record (c) 2006 APA, all rights reserved)