Mood states of cancer patients were assessed pre- and post-41.8 degrees C whole-body hyperthermia using the Profile of Mood States questionnaire. Results demonstrated a statistically significant increase in fatigue associated with decreased vigour which returned to baseline values by 72 h. In contrast, a significant improvement in depression was evident through 72 h following treatment. The relationship of this result to earlier studies of WBH-induced beta-endorphin is discussed.