Fatty acid-binding protein (FABP) is a newly introduced plasma marker of acute myocardial infarction (AMI). The plasma kinetics of FABP (15 kD) closely resemble those of myoglobin (18 kD) in that elevated plasma concentrations are found within 3 h after AMI and return to normal generally within 12 to 24 h. This makes both myoglobin and FABP useful biochemical markers for the early assessment or exclusion of AMI. The myocardial tissue content of FABP (0.5 mg/g) is about five-fold lower than that of myoglobin (2.5 mg/g), but the reference plasma concentration of FABP (ca. 2 microg/l) is about 15-fold lower than that of myoglobin (ca. 32 microg/l), together suggesting a superior performance of FABP for the early detection of AMI. Indeed, in a study including blood samples from 83 patients with confirmed AMI, taken immediately upon admission to the hospital (< 6 h after AMI), the diagnostic sensitivity was significantly greater for FABP (78%, confidence interval 67-87%) than for myoglobin (53%, CI 40-64%) (P < 0.05). In addition, the differences in contents of myoglobin and FABP in heart and skeletal muscles and their simultaneous release upon muscle injury allow the plasma ratio of myoglobin/FABP to be applied for discrimination of myocardial (ratio 4-5) from skeletal muscle injury (ratio 20-70). Rapid and sensitive immunochemical assay systems for FABP in plasma are now being developed and soon will enable the introduction of this marker in clinical practice.