We compared the diagnostic utility of serum concentrations of human heart-type cytoplasmic fatty acid-binding protein (H-FABPc), myoglobin, and their ratio for the early diagnosis of acute myocardial infarction (AMI) in 104 healthy volunteers and 165 patients at admission within 6 h of the onset of chest pain. The ROC curves of the H-FABPc [0.946, 95% confidence interval (CI) = 0.913-0.979] and myoglobin (0.895, 95% CI = 0.846-0.944) between patients with AMI and healthy volunteers were significantly greater than the area under the ratio of myoglobin to H-FABPc (0.823, 95% CI = 0.765-0.881). In 165 patients, the sensitivity (81.8%, 95% CI = 74.2-89.4%), specificity (86.4%, 95% CI = 78.1-94.6%), and predictive accuracy (83.6%, 95% CI = 78.0-89.3%) of H-FABPc > 12 micrograms/L in diagnosing AMI were significantly higher than those of myoglobin, and were similar to those of the combination of H-FABPc > 12 micrograms/L and the ratio < or = 14. We conclude that H-FABPc is a more sensitive and specific marker than myoglobin for the early diagnosis of AMI, and that their ratio cannot give a clear advantage over the measurement of H-FABPc alone.