We prepared two monoclonal antibodies-A-I30 and A-I4 to HDL apo A-I-with the ultimate goals of expressing and overproducing the valuable immunodiagnostic single chain Fv by phage display libraries in E, coli. Monoclonal antibodies were produced by immunizing mice with apolipoprotein A-I, and purified from ascitic fluid by affinity chromatography on a Protein A Sepharose CL-4B column. The specificity of A-I30 and A-I4 was confirmed by ELISA and Western blotting. The dissociation constants(Kd) of antigen-antibody complex obtained by enzyme linked immunosorbent assay(ELISA) method were 2.25 x 10(-8) M for A-I30 and 2.15 x 10(-8) M for A-I4. The experimental values of Kd are shown to be close to those obtained by immunoprecipitation of the radiolabeled antigen. From the above results, it was shown that A-I30 and A-I4 could be provided as excellent reagents for the determination of plasma HDL concentrations in clinical specimens using ELISA.