This study attempted to determine the effects of interval and continuous running on factors associated with cardiovascular health. Fifty-nine untrained men and women, ages 18-32 years, were randomly assigned to one of four groups: (1) 4 mile: running continuously at 75% of maximal heart rate (approximately 500 Cal/session) (2) 2 mile: running continuously at 75% of maximal heart rate (approximately 250 Cal/session) (3) interval: running one min at 90% maximal heart rate followed by three min of walking for eight sets (approximately 500 Cal/session) (4) control: no exercise program. The training was performed three times per week for 12 weeks. Treadmill VO2 max and percent body fat by hydrostatic weighing were assessed pre- and post training. Pre and post analyses were performed on plasma for triglycerides (TG), cholesterol (Chol), and high density lipoprotein cholesterol (HDL-C). Analysis of covariance indicated that only the interval group improved more than the control in VO2 max. Percent fat decreased in all exercise groups, but no program was superior. Changes in TG, Chol, or HDL-C were not different among groups. Although men and women differed on the pretests in VO2 max, percent fat, and HDL-C, their response to the training was similar. These results indicate that interval training may benefit aerobic capacity more than continuous running in young adults who have moderately high initial fitness levels. The data also indicate that cardiovascular fitness parameters are not easily altered by short term exercise in young active men and women.