We measured serum hepatocyte growth factor (HGF) in patients with acute myocardial infarction, angina pectoris, and other heart diseases. In patients with acute myocardial infarction, blood was collected at the time of admission. Serum HGF was elevated within 3 hours in 8 of 10 patients (80%) with acute myocardial infarction after onset of chest pain (9.4 ± 3.2 ng/mL, mean ± SEM, values in normal subjects <0.39 ng/mL). Mean value of serum HGF was 11.0 ± 2.6 ng/mL (n = 11) in patients who admitted to the hospital between 6 and 9 hours and 13.1 ± 5.7 ng/mL between 12 and 24 hours after onset. Elevated HGF levels were significantly more frequent than those of creatine kinase within 3 hours, and elevated levels correlated well with those of serum creatine kinase at 6–9 hours after onset of acute myocardial infarction. No increase in serum HGF value was found in patients with angina pectoris or other heart diseases. Thus, measurement of HGF is a sensitive method for early diagnosis of acute myocardial infarction.