Endothelial progenitor cells (EPCs) and late outgrowth endothelial cells (OECs) seem to play an important role in vessel formation. While EPCs seem to exert their function mainly through a paracrine effect, the OECs can develop into mature endothelial cells and form tubular structures. Exercise is known to increase angiogenic factors that can mobilize EPCs; however, the effect on OECs is not known. We investigated the response to a single session of strenuous exercise on OECs, vascular endothelial growth factor (VEGF) and inflammatory cell levels in the healthy. Eleven healthy subjects performed 1 h of spinning exercise. Blood samples were collected at 1, 6, 24 and 48 h post-exercise for cell culture and biochemical analysis. OEC colonies doubled one hour after the spinning session (baseline 4.5 +/- 4.3 vs. 9.0 +/- 3.7, P < 0.05). Serum VEGF increased from 194 +/- 107 pg/ml at baseline to 224 +/- 111 pg/ml after 1 h, p = ns and neutrophilic granulocytes increased from 3.73 +/- 1.38 at baseline to 9.08 +/- 10.5 at 1 h (P < 0.01). The increased levels of OECs, VEGF and neutrophilic granulocytes declined gradually at the following time points. VEGF levels and neutrophilic granulocytes were highly correlated to OEC levels, r = 0.903 (VEGF) and r = 0.85 (neutrophilic granulocytes), respectively. Strenuous physical activity increases OEC colonies and is correlated to serum VEGF and neutrophilic granulocytes levels. An acute exercise-induced inflammatory response might be responsible for the VEGF release and subsequent increase of OECs. The clinical importance of these findings remains to be elucidated.