Endothelial progenitor cells were isolated from peripheral blood obtained from 32 healthy volunteers without cardiovascular risk factors who ranged in age from 20 to 61 years (mean [+/- SD] age, 34.1 +/- 9.6 years). The fractions of CD34(+) endothelial progenitor cells expressing kinase insert domain receptor-1, CD62E, or CD31 were analyzed with flow cytometry. Correlation analysis demonstrated that there was no significant correlation between subject age and the fraction of circulating CD34(+) mononuclear cells expressing kinase insert domain receptor-1 (P = 0.324; r = -0.180). Similarly, there was no significant correlation between subject age and the fraction of circulating CD34(+) mononuclear cells expressing CD62E (P = 0.496; r = -0.125) or the fraction of circulating CD34(+) mononuclear cells expressing CD31 (P = 0.245; r = -0.212). In conclusion, the experimental results showed that there was no age-related change in the basal level of circulating endothelial progenitor cells in healthy subjects without cardiovascular risk factors.