Hybridoma cell lines secreting monoclonal antibodies to human serum apo (a) were produced by lymphocyte hybridoma technique. Sandwich enzyme-linked immunosorbent assay (ELISA) for determining lipoprotein (Lp) (a) concentration were established with monoclonal or polyclonal antibodies: the first ELISA was performed by using polyclonal antibody to apo (a) as the capture and quantitating antibody, the second by using polyclonal antibody to apo B as the capture antibody and quantitating the bound Lp (a) particles with antibody to apo (a). ELISA by using a single and mixed monoclonal antibodies were established also. We measured and analysed the serum Lp (a) levels, the results indicated that differences between the values obtained by different methods are dependent on the size of the apo (a ) isoform in the sample.