We have described the responses of selected hormones [luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol (E2), progesterone (P), androstenedione (delta 4-A), testosterone (T)] and substrates (glucose, lactate) before, during, and after a marathon run in five women of varying gynecological status. Blood samples (15 ml) were obtained 60 and 30 min before the race, during the race at 10, 20, and 30 km, and after the race at min 5, 60, and 120. The relative intensity of running varied between 60% and 85% VO2 max, and weight loss ranged from 2.6 to 3.0 kg. The new observations from our data include the fact that FSH was increased during exercise, whereas this was not observed for LH. This latter hormone appears to be linked more closely to the exercise intensity as defined by blood lactate increments. Increments occurred in all steroid hormones and paralleled those observed in controlled laboratory studies, although the magnitude of these changes was larger at the end of the marathon run. Except for dehydroepiandrosterone sulfate (DHEA-S), most of the hormones returned to basal levels in the 2 h after the marathon. DHEA-S exhibited no change until the 30-km point, when a sharp increase was observed, and then remained elevated for 2 h after exercise, suggesting that a) adrenocortical production of steroids continues for a long time after exercise, b) there is a marked reduction in hepatic clearance of this hormone. In summary, the present study shows that prolonged exercise has a marked effect on both steroid and pituitary hormones.