Concentration of lipoprotein(a) in plasma is inherited in an autosomal co-dominant manner and its high concentration leads to atherothrombotic disease. Nucleotide sequence analysis of the apolipoprotein(a) gene revealed the presence of polymorphisms in its 5'-flanking region, which can be analyzed by in vitro amplification employing gene-specific primers. Genomic DNAs from normal individuals have been subclassified into four alleles according to the patterns of restriction digestion. The ratios of these subtypes differed between Caucasians and Japanese and in patients with myocardial infarction. It is very likely that the 5'-alleles in part control the plasma lipoprotein(a) level.