We studied the effect of emotional stress (mental arithmetic for 10 minutes) in ten postinfarction patients and in ten age-matched, apparently healthy subjects as controls. Blood samples for the determination of epinephrine and AT III levels were taken in basal conditions, at the end of mental stress and after 30 minutes of recovery. Mental stress induced a significant increase in epinephrine levels and a significant decrease in AT III levels in control subjects. Both parameters returned to baseline values after 30 minutes of recovery. On the contrary, in postinfarction patients AT III levels of recovery were still significantly lower than those of baseline, suggesting a reduced ability to restore the original concentration of this physiologic inhibitor. Our data can contribute to a better understanding of the complex relationships among phychosocial factors, the haemostatic system and vascular disease.