Cortisol is essential for regulating all cell types in the body, including those in the brain. Most information concerning cortisol's cerebral effects comes from work in nonhumans. This is a first effort to use functional magnetic resonance imaging (fMRI) to study the time course and locus of cortisol's effects on selected brain structures in resting humans. We repeatedly scanned 21 healthy young adults over 45 min to examine changes in the brain's activity 5 min before, and for 40 min after, an IV injection of 10mg of hydrocortisone (N=11) or saline placebo (N=10). At 15-18 min postinjection we observed in the hydrocortisone group reduced activity in the hippocampus and amygdala that reached a peak response minimum at 25-30 min postinjection (-1 Standard Deviation) relative to placebo. No such effect was seen in the thalamus. Functional MRI appears to be a safe, noninvasive method to study the time course and anatomical effects of glucocorticoids in the human brain.