We tested the hypothesis that priming exercise would speed V(O2) kinetics during treadmill running. Eight subjects completed a square-wave protocol, involving two bouts of treadmill running at 70% of the difference between the running speeds at lactate threshold (LT) and V(O2) max, separated by 6-min of walking at 4 km h(-1), on two occasions. Oxygen uptake was measured breath-by-breath and subsequently modelled using non-linear regression techniques. Heart rate and blood lactate concentration were significantly elevated prior to the second exercise bout compared to the first. However, V(O2) kinetics was not significantly different between the first and second exercise bouts (mean+/-S.D., phase II time constant, Bout 1: 16+/-3s vs. Bout 2: 16+/-4s; V(O2) slow component amplitude, Bout 1: 0.24+/-0.10 L min(-1)vs. Bout 2: 0.20+/-0.12 L min(-1); mean response time, Bout 1: 34+/-4s vs. Bout 2: 34+/-6s; P>0.05 for all comparisons). These results indicate that, contrary to previous findings with other exercise modalities, priming exercise does not alter V(O2) kinetics during high-intensity treadmill running, at least in physically active young subjects. We speculate that the relatively fast V(O2) kinetics and the relatively small V(O2) slow component in the control ('un-primed') condition negated any enhancement of V(O2) kinetics by priming exercise in this exercise modality.