This study presents 3 years of data from a longitudinal study designed to follow changes in VO2max and treadmill (TM) exercise performance in African-American girls throughout middle school. Subjects (N = 19) were tested 6 months apart during grades 6-8. VO9 and heart rates (HR) were measured continuously while each subject performed an incremental TM test to volitional exhaustion. Absolute VO2max (ml • min1) increased with time, while relative (ml • kg 1 * min1) values declined significantly from 6th to 8th grade. Treadmill time to exhaustion improved after the first test, but showed a significant decline by the end of 8th grade. Correlations between fall 6th-grade and spring 8th-grade aerobic fitness measures ranged from .35 to .57, indicating moderate tracking of these variables throughout middle school. Aerobic fitness values are low (compared to Caucasians) in African-American adolescent girls and show significant declines throughout middle school. Future studies should investigate anatomical, physiological, and behavioral reasons for the apparently low aerobic fitness seen in African-American girls.