Aim To investigate the effects of asymmetric dimethylarginine(ADMA)on the proliferation of endothelial progenitor cell(EPC)of human umbilical cord blood and observe whether L-arginine can antagonize the effects of ADMA.Methods Mononuclear cells were isolated from fresh cord blood and cultured for 7days,attached cells were incubated with different concentration of ADMA(1,5 and 10 μmol/L)among different times(24,48 and 72 h).MTT assay was used and colony forming units(CFU)were quantified to evaluate the proliferation of EPC after treated with ADMA.Meanwhile,MTT assay was used and DiI-acLDL uptake cells under high-power field of fluorescence microscopy were quantified to assay effects of L-arginine on ADMA-induced EPC proliferation.Nitric oxide(NO)and nitric oxide synthase(NOS)in the supernatant were measured by nitrate reductase assay and chemical colorimetry assay.Results Incubation of EPC with ADMA dose and time-dependently decreased the number and the proliferation of EPC.In addition,the depressant effect of ADMA on EPC were dismissed with the inceasing dosage of L-arginine.Conclusions It is suggested that ADMA can promote endothelial dysfunction by means of depressant EPC proliferation and exogeno L-arginine maybe antagonize the effects of ADMA.