As a possible reflection of central norepinephrine metabolism, urine MHPG excretion was measured in naval aviators during aircraft carrier landing practice, a complex task and a stress of considerable magnitude. Mean urine MHPG was significantly increased after both day and night carrier landings compared to a nonflying control day. These findings suggest that there may be an accelerated metabolism of brain norepinephrine under conditions of heightened arousal and concentration compared to the normal waking state.