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The purpose of this experiment was to examine the blocking effect within the context of a stimulus equivalence paradigm. Ten subjects were provided with a prior history of matching unitary sample stimuli to unitary comparisons. Next, the same stimuli appeared as elements of sample stimulus compounds with additional, redundant elements. During the equivalence test, the elements of each compound were separated, and the extent to which the elements had entered separately into equivalence relations with the other stimuli was examined. Five subjects demonstrated the formation of three three-member equivalence classes and showed a strong blocking effect. The other five subjects did not demonstrate the formation of three-member classes, nor did they show a strong blocking effect. The strength of the relations between the elements of each stimulus compound was shown to be consistent with the degree to which the blocking effect was observed. Subjects' percentage reinforcement estimates were also found to correspond to their performance during the equivalence test. The overt verbal behavior emitted by four subjects who were required to talk aloud during the experiment did not correlate with their nonverbal performance.