There are conflicting data with regard to the effect of endurance training in children. On the basis of this information, the effects of 8 wk of run training on ventilatory threshold (VT) and &OV0312;O2maxof eight male children were investigated. Children ranged in age from 10 to 14 yr, with a mean age of 12.4 yr. All subjects were previously untrained. Training consisted of running 4 d·wk−1for a period of 8 wk. Continuous running was performed 2 d·wk−1for 10–30 min at 70–80% of &OV0312;O2max. Interval running was performed the remaining 2 d·wk−1. Repeated intervals of 100–800 m at 90–100% of &OV0312;O2maxwere used in this phase of the training. The total distance run for this type of training was 1.5–2.5 km. Incremental treadmill testing prior to and after the training period indicated a 19.4% increase in VT from 30.5 to 36.4 ml·kg−1·min−1(P < 0.05). When VT was expressed as a percentage of &OV0312;O2max, there was a significant (P< 0.05) increase from 66.6% to 73.8%. &OV0312;O2maxincreased 7.5% from 45.9 to 49.4 ml·kg−2·min−2(P< 0.05). None of these changes was noted in eight age- and size-matched children who served as control subjects. The results of this study indicate that 8 wk of endurance running training which is of sufficient frequency, intensity, and duration can significantly improve VT and aerobic capacity in made children.