Our research group has observed in an open trial that a single session of whole body hyperthermia (WBH) induced rapid antidepressant effects that persisted for at least a week in patients with major depression (MDD) severe enough to warrant inpatient hospitalization. In addition to reducing depression, the single session of WBH induced a prolonged reduction in mean core body temperature, consistent with basic science data from our group suggesting that hyperthermia activates a skin-to-brain pathway that targets specific serotonergic nuclei in the raphe. In animal models, these nuclei have been shown to be important for mood and body temperature regulation. Consistent with this known anatomy in our preliminary study in depressed patients, reductions in core body temperature were highly correlated with reductions in depressive symptoms over the same time period (one week post WBH). Moreover, patients with higher mean core body temperature prior to treatment had enhanced antidepressant effects. Because increased body temperature is an outcome of poor functioning in the skin-to-brain pathway activated by WBH our data suggests that WBH may actually sensitize this pathway in ways that promote changes in brain functioning known to promote emotional well-being. The results of our first open trial have encouraged us to conduct a larger, more rigorous placebo-controlled, double blind study of WBH for MDD, which is currently underway at the University of Arizona Medical School.