The purpose of this investigation was to examine whether psychological responses to exhaustive exercise would vary if the exercise was performed in the AM or PM. Sixteen men completed the State-Trait Anxiety Inventory and the Profile of Mood States before and following two exhaustive exercise sessions in the AM (0630-0930h) and the PM (1700-2000h). Data were analyzed with a 2 (condition = incremental, constant) x 2 (time of day = AM, PM) x 2 (trial = pre, post) repeated measures ANOVA. Results indicated that there was a significant time of day effect (P<0.05), as well as a significant condition by trial interaction (P<0.05) for vigor. Vigor was found to he higher in the PM before the constant power exhaustive exercise session, and decrease significantly following the session. There was also a significant trial effect (P<0.05) for fatigue. Fatigue was found to increase following the constant power exhaustive exercise sessions in the AM and PM. There were no significant changes in state anxiety, tension, depression, anger confusion or the composite measure of mood following exhaustive exercise in the AM or the PM. It is concluded that anxiety and mood responses to brief exhaustive cycling exercise are similar whether the exercise is performed in the morning or evening.