Although the role of humor in relaxation and interpersonal relationships is well documented, its role in increasing performance in the classroom has not been systematically studied. To investigate the effect of appropriately timed humor on performance of a stressful task, 40 college students performed a mathematics test under one of four experimental conditions (high or moderate stress; presence or absence of humor). The procedure entailed a pretest administration of the stressor (the Quiz Electrocardiogram) combined with the dependent measure, a 7-minute break during which the humor/no humor condition was implemented, and a post-break readministration of the stressor with the dependent measure. An analysis of the results showed that humor did not significantly reduce ratings of complexity, time constraint, or ego involvement in high or low stress conditions. However, both the main effect for humor and the humor by stress interactions were statistically significant, indicating that humor improved the level of subsequent task performance. These findings confirm the effectiveness of humor on task performance; however, the underlying mechanisms of that interaction need further clarification. (BL)