We assessed the changes in plasma von Willebrand factor level concentration in 10 patients with Q-myocardial infarction and in six patients with non-Q-myocardial infarction who did not receive thrombolytic treatment. Concentrations of von Willebrand factor antigen were measured by an enzyme-linked immunoassay method in plasma samples obtained twice daily for 4 consecutive days. In patients with Q-wave myocardial infarction, a significant rise in von Willebrand factor antigen levels (P < 0.05) occurred after admission and persisted for 3 days. No significant changes were found in plasma concentration of fibrinogen. In conclusion, von Willebrand factor antigen levels were greater in patients with Q-wave compared to patients with non-Q-wave myocardial infarction.