Objective To investigate the role of dimethylarginine dimethylaminohydrolase-2 (DDAH-2)/asymmetric dimethylarginine(ADMA)in pathophiology of preeclampsia by detecting expression of DDAH-2 in placenta and serum plasma ADMA.Methods From Jan.2004 to Jan.2005,30 preeclampsia patients(PE group)were chosen in the Third Affiliated Hospital.Guangzhou Medical College matched with 10 normal third trimester women as control(control group).The placental DDAH-2 mRNA expression was detected by fluorescence quantitative polymerase chain reaction(FQ-PCR)and the plasma concentration of ADMA WSB determined by high performance liquid chromatography(HPLC).Results(1)The level of ADMA in PE group was significantly higher that than of control group[(18.0±7.2)mg/L vs.(10.3±1.7)mg/L,P<0.01].The expression level of ADMA in preeclampsia occurring before 34 gestatinal weeks WaS significantly higher than that of preeclampsia occurring after 34 gestational weeks[(22.0±7.0)ms/L vs.(12.7±2.8)mg/L,P<0.01].(2)The Placental DDAH-2 mRNA expression in preeclampsia patients was remarkably lower than that of control group[1×10(5.23±0.45)copy/μlvs.1×10(5.65±0.08)copy/μl,P<0.01].The Placental DDAH-2 mRNA in preeclampsia occurring before 34 gestatinal weeks was significantly lower than that of preeclampsia occurring after 34 gestational weeks [1×10(5.02±0.46)copy/μl vs.1×10(5.61±0.19)copy/μl,P<0.01].Conclusion Our results suggested that low expression of DDAH-2 in placenta and increased serum ADMA level might confer the susceptibility to preeclampsia.