The epitopes of plasminogen (Pg) of serum lipoprotein(a)［Lp(a)］［Lp(a)-Pg］ were determinated by ELISA using monoclonal anti-apo(a) as the capture antibody and quantitating with anti-Pg enzyme conjugate. The assay range by this method was from 28 to 880 mg/L. The mean intra- and inter-assay coefficients of variation were 4%～6% and 7%～9%, respectively. The serum Lp(a) concentration was positively correlated with serum Lp(a)-Pg level and negatively with Lp(a)-Pg level to total Lp(a) ［Lp(a)-Pg/Lp(a)］ ratio. Serum Lp(a) concentration, Lp(a)-Pg level and Lp(a)-Pg/Lp(a) ratio were found significantly elevated in CHD and CRF patients compared with those in the controls. Determination of Lp(a)-Pg level and Lp(a)-Pg/Lp(a) ratio in patients with high incidence of atherosclerosis have special value.