Twenty female and 45 male middle and long-distance runners, in training for the U.S. Olympic Trials, served as subjects. Ninety percent of both men and women subjects reached the Trials; eight women and 12 men qualified for the Olympic Games and five won medals. Each subject completed a VO2max and a series of submax treadmill runs, for the purpose of comparing heart rate (HR), VO2, and blood lactate (HLa) among men and women and among runners of various event specialties. Results showed the men to be taller, heavier, to have a lower six-site skinfold sum and a higher VO2max, than the women (P less than 0.05); there was no difference in age. When compared in running economy, men used less oxygen (ml.min-1.kg-1) at common absolute velocities, but VO2 (ml.km-1.kg-1) was not different between men and women at equal relative intensities (%VO2max). When men and women of equal VO2max were compared, the men were significantly more economical, using any method of comparison. Also, when comparisons of men and women of equal economy were made, it was found that the men had an even greater advantage over the "matched" women subjects than the mean VO2max comparison using all subjects. In looking at the SD (800-/1500-m runners), MD (3-K/5-K/10-K runners) and LD (marathon runners), it was found that the SD runners used the least oxygen (ml.min-1.kg-1) at speeds of marathon race pace and faster, but not at slower speeds. Men and women responded similarly in this regard. Running economy data for speeds slower than typical race paces, tended to show the LD runners to be most economical, suggesting that the speeds over which runners are tested plays an important part in determining which subjects are the most economical. It was concluded that at absolute running velocities, men are more economical than women, but when expressed in ml.km-1.kg-1 there are no gender differences at similar relative intensities of running. Also, when men and women of equal VO2max or equal economy are matched, the men show a better aerobic profile. It is recommended that economy data be collected up to speeds equal to over 90% VO2max.