NUMBER OF FOOD PELLETS (REWARD MAGNITUDE HELD CONSTANT) WAS VARIED ORTHOGONALLY WITH 5 PARTIALLY OR CONTINUOUSLY REWARDED ACQUISITION TRIALS IN MALE WISTAR RATS. SIGNIFICANT ACQUISITION OCCURRED. WITH 1 OR 2 PELLETS, THERE WAS A TENDENCY TOWARDS GREATER RESISTANCE TO EXTINCTION AFTER CONTINUOUS REINFORCEMENT; HOWEVER, WITH EITHER 10 OR 24 PELLETS, A SIGNIFICANT PARTIAL REINFORCEMENT EFFECT (PRE) WAS OBTAINED. THESE DATA ARE DISCUSSED IN TERMS OF THEIR RELEVANCE TO PREVIOUS DEMONSTRATIONS OF THE PRE AFTER MINIMAL ACQUISITION, AND TO A FRUSTRATIVE NONREWARD INTERPRETATION OF PARTIAL REINFORCEMENT PHENOMENA. (PsycINFO Database Record (c) 2006 APA, all rights reserved)