We investigated the role of emotional stress in the relationship with plasma catecholamines and platelet function in patients with ischemic heart disease. The degree of subjective stress, plasma catecholamines, whole blood platelet aggregation and plasma β-thromboglobulin (βTG) were determined in 45 patients with angina pectoris (AP group), 40 patients with old myocardial infarction (OMI group) and 50 healthy individuals (control group). The degree of emotional stress was measured by recording subjective stress of 4 degrees (0 : without stress, 1 : with mild stress, 2 : with moderate stress, 3 : with severe stress) every one hour and these values of every hour of the day were summed up. Subjective stress (stress score) were determined by average values of 6 days. The levels of epinephrine (EP) and norepinephrine (NE) were determined by high-performance liquid chromatography with an electrochemical detector, and βTG by radioimmunoassay. Whole blood platelet aggregation was measured by impedance method. Stress scores of AP group and OMI group (7.86±6.43,8.95±5.03,respectively) (mean±SD) were significantly higher than that of control group (4.08±2.90). There was no significant difference of the contents of EP and NE between these three groups. Whole blood platelet aggregation of AP group and OMI group (17.4±4.7,16.9±3.8,respectively) were significantly elevated compared with that of control group (13.4±4.4). The contents of βTG of AP group and OMI group (32.9±18.3 ng/ml, 33.3±16.4,respectively) were also increased significantly compared with that of control group (22.5±12.5). Then plasma catecholamine levels and platelet function were compared between the high stress group (stress score above 7) and the low stress group (stress score less than 7) of AP and OMI patients. The content of EP of the high stress group (0.036±0.015) were significantly higher than that of the low stress group (0.025±0.013) but there was no significant difference in the contents of NE of the high stress group and the low stress group. Whole blood platelet aggregation of the high stress group (19.3±5.1) was higher than that of the low stress group (14.5±4.0) significantly, and the level of βTG of the high stress group was also higher than that of the low stress group. These results suggest that emotional stress in patients with ischemic heart disease is higher than that of the control group and platelet function is accelerated. In the high stress group, plasma EP level and platelet function were elevated compared with the low stress group. So it was concluded that emotional stress is closely related to the development of ischemic heart disease at least in part by influencing the catecholamines and platelet function.