An experiment was conducted to investigate the relative merits of in vivo emotive imagery and performance feedback in enhancing self-efficacy beliefs and performance on a competitive muscular endurance task. College males (n=60) and females (n=60) were randomly assigned to one of three conditions: mastery imagery plus feedback, feedback alone, or control condition. Subjects in the imagery-plus-feedback condition were told that one of the pair (always the subject) would receive imagery exposure while the other (always the confederate) would wait outside. Subjects performed two trials against the confederate, who always won by 10 seconds. A Group x Trials interaction for self-efficacy revealed a significant increase for the imagery group after brief exposure. Also, imagery subjects had significantly higher efficacy scores than feedback alone or control subjects after each performance trial. A Group x Trials interaction for performance indicated that imagery subjects initially had significantly longer performance times than did feedback alone or control subjects. Performance feedback alone did not influence efficacy beliefs or performance.