It has been shown previously that accumulation of homocysteine produces atheromatous changes. The present study was done on 26 male survivors of myocardial infarction 2-3 months after the acute phase and 26 healthy males of the same age (30-60 years). The concentrations of homocysteine, its derivatives and other amino acids were determined in acid hydrolyzate of plasma and in deproteinized plasma. The plasma proteins of survivors of myocardial infarction were found to contain a high concentration of homocysteine. The average value was 958 +/- 84 mumol/l of plasma, which was about 25 times the quantity found in the control group. Large differences were also found in alpha-amino adipic acid and cystathionine concentrations. These substances were found in significantly higher concentrations in the plasma of the survivors compared to controls. The high positive correlation between homocysteine and alpha-amino adipic acid level (r = 0.83; P less than 0.001) suggests a common source of these 2 compounds in the analyzed samples. The levels of the other 15 measured amino acids were not significantly different in the 2 groups. The results support the homocysteine theory and suggest a method for more exact diagnosis of atherosclerosis.