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Four experiments with rat subjects asked whether a partial reinforcement extinction effect (PREE) occurs in taste aversion learning. The question has received little attention in the literature, and to our knowledge no taste aversion experiment has previously demonstrated a PREE. In each of the present experiments, experimental groups received a taste mixed in drinking water for 20 min; such taste exposures were sometimes paired with a lithium chloride (LiCl) injection and sometimes not. Control groups received only taste-LiCl pairings. There was evidence that each reinforced and non-reinforced trial produced increments and decrements in aversion strength (respectively), and trials mattered more than accumulated time during the conditioned stimulus and during the background (as emphasized in time-accumulation models like those of Gallistel and Gibbon, Psychological Review, 107, 289-344, 2000, and Gibbon and Balsam, Autoshaping and conditioning theory, Academic Press, New York, pp. 219-235, 1981). In addition, a partial reinforcement extinction effect was observed when there was a relatively large number of conditioning trials. The results extend our understanding of extinction in taste aversion learning and provide more evidence that aversion learning might follow rules that are qualitatively similar to those of other forms of learning. [ABSTRACT FROM AUTHOR]