Fifty-six consecutive patients, 53 males and 3 females aged from 36 to 83 with a mean age of 61.0, all with acute myocardial infarction (AMI), were screened for anticardiolipin antibodies (ACA) by single sampling at time of admission to the medical intensive care unit; results were compared with those for age-matched, healthy controls. IgM and IgG-ACA were measured by an enzyme-linked immunosorbant assay technique. IgG-ACA were detected in 9 patients (16.1%); IgM-ACA were detected in 9 patients (16.1%). Only one of the patients had raised ACA of both isotypes. There was on difference in either ACA levels or frequency of ACA elevation between patients and controls. Risk factors of coronary artery disease showed no significant difference between patients with and without ACA. Low titer of IgG-ACA was found in one of ten patients with reinfarction and/or previous cerebral infarction. In conclusion, single measurements of anticardiolipin antibodies in general AMI patients are unlikely to yield diagnostically important information. The implication of occasional significant elevation of such antibodies in a general AMI population remains to be speculated.