The study was undertaken to measure plasma interleukin-1 (IL-1) receptor antagonist and IL-10 concentrations in patients with acute myocardial infarction and to analyze their relationship to the hemodynamics, severity, and prognosis of myocardial infarction in its acute stages. We attempted to define the kinetics of IL-1 receptor antagonist and IL-10 in patients with acute myocardial infarction (n = 34, age 42-91 years, mean 68 years). Plasma IL-1 receptor antagonist and IL-10 levels were measured by enzyme-linked immunosorbent assay. Patients in group A (n = 17) had uncomplicated acute myocardial infarction (Killip class I). Patients in group B (n = 17) had severe acute myocardial infarction (Killip class II, III, or IV). Peak Il-1 receptor antagonist and IL-10 levels in group B were significantly higher (p < 0.05) than those of group A. In group B, the peak IL-1 receptor antagonist levels were significantly correlated with white blood cell counts (r = 0.63, p = 0.006), pulmonary capillary wedge pressure (r = 0.78, p = 0.0002), and cardiac index (r = -0.51, p = 0.04). Peak IL-10 levels were significantly correlated with white blood cell counts (r = 0.60, p = 0.01), the pulmonary wedge pressure (r = 0.73, p = 0.0008), and cardiac index (r = -0.50, p = 0.04). Moreover, a significant correlation was found between the peak IL-1 receptor antagonist and IL-10 levels (r = 0.91, p < 0.0001). The peak IL-1 receptor antagonist levels in nonsurvivors (n = 13) were significantly higher (p < 0.01) than those in survivors (n = 21). The plasma IL-1 receptor antagonist and IL-10 levels were closely correlated with the severity of hemodynamics in acute myocardial infarction and with the clinical status of patients with severe acute myocardial infarction. Results suggest that plasma IL-1 receptor antagonist and IL-10 can serve as prognostic indicators in cases of sever acute myocardial infarction.