A rapid latex agglutination test for the detection of elevated levels of myoglobin in serum was evaluated in a prospective study of 236 patients consecutively admitted to a Coronary Care Unit on suspicion of acute myocardial infarction (AMI). The final diagnosis was made according to the WHO criteria. The prevalence of AMI was 0.45 with a male to female ratio of 2:1. In all patients at least two blood samples were collected with 4 hours interval 4-12 hours after the onset of symptoms. All sera were analysed for myoglobin by a latex agglutination test and by a radioimmunoassay (RIA). The latex test was performed twice, first as an emergency test by the technical assistant on duty and later by another well-trained technical assistant as her daily routine work. If the latex test was carried out each day by the same well-trained technical assistant, the test results agreed well with the RIA test results, and the false-negative fraction for patients with AMI constituted 0.06 and the false-positive fraction for patients without AMI 0.46. However, when the latex test was performed by the occasional technical assistant on duty, a relatively high degree of discrepancy was observed between the latex test results and the RIA test results, thus giving a false-negative fraction of 0.11 and a false-positive one of 0.36. In conclusion, performed under optimal laboratory conditions, the latex test can be used as a reliable method to estimate elevated levels of serum myoglobin. However, used as a bedside emergency examination, the test results correlated rather poorly to the RIA test results, and consequently the latex myoglobin test seems to be of minor clinical importance in the early evaluation of patients with suspected AMI.