To evaluate whether polymorphisms in the 5' region of the apolipoprotein(a) gene alter the risk for myocardial infarction, 289 Russian male patients with myocardial infarction (MI) and 284 subjects in a control group were investigated regarding the distribution of pentanucleotide repeats (PNRs) at position -1373 and a C/T transition at position +93. For detection of the C/T (+93) allele, we developed a rapid, nonisotopic method by mismatch PCR-mediated site-directed mutagenesis and restriction enzyme digestion. We observed significant differences in prevailing alleles with over eight (TTTTA) repeats among MI patients, including those with MI younger than 55 years of age. We observed the prevalence of the T (+93) allele in children without a family history of CHD compared to young MI patients. These findings support the notion that PNR alleles with over eight (TTTTA) repeats may play a pathogenic role, and the T (+93) allele may have a protective effect for the inherited predisposition to heart disease.