Abstract After acid hydrolysis, mean plasma homocysteine concentrations, measured as homocysteine disulphides, of about 1000 and 40 μmol/l have recently been reported in 26 survivors of myocardial infarction and 26 matched control subjects, respectively. This finding contrasts sharply with those more than 50 times lower total homocysteine concentrations found by other research groups in non-hydrolysed plasma from survivors of myocardial infarction. Using the same hydrolysis conditions, we could not detect any homocysteine disulphides in plasma hydrolysates from 9 survivors of myocardial infarction and 10 healthy subjects, who had mean total homocysteine concentrations in non-hydrolysed plasma of 16.9 ± 6.5 and 15.8 ± 10.3 μmol/l, respectively. The chromatograms contained several peaks, probably representing peptides, which disappeared with more complete hydrolysis and which might have been misinterpreted as homocysteine disulphides in the reported study. Only after reduction of disulphides and by using a sulphydryl-selective extraction procedure were we able to determine mean homocysteine concentrations in hydrolysed plasma to be 26.2 ± 7.9 μmol/l in the survivors of myocardial infarction and 24.5 ± 12.2 μmol/l in the healthy reference subjects. Thus, we could not confirm that survivors of myocardial infarction have homocysteine concentrations that are many times higher than found in healthy subjects.