To verify whether beta-endorphin plasma levels influence the presence of anginal symptoms, 74 consecutive male patients were studied. All patients had previously documented coronary artery disease and reproducible exercise-induced myocardial ischemia. Thirty-five patients (Group I) had a history of angina and reported anginal symptoms during exercise stress testing; 39 patients (Group II) were asymptomatic and had documented silent myocardial ischemia during exercise. Baseline beta-endorphin plasma levels were measured in blood samples taken before exercise stress testing and analyzed by beta-endorphin-I125-RIA Kit-NEN (a radioimmunoassay method). The mean baseline beta-endorphin plasma level was 22.5 +/- 19 pg/ml in patients with anginal symptoms compared with 43.7 +/- 28 pg/ml in asymptomatic patients (p less than 0.001). Baseline blood pressure and heart rate-systolic pressure (rate-pressure) product at baseline and at ischemia threshold (1 mm ST segment depression) were similar in the two groups. Group II patients had a longer exercise duration (p less than 0.01), more pronounced ST segment depression (p less than 0.001) and a higher peak rate-pressure product (p less than 0.01). The extent of coronary artery disease, ejection fraction and left ventricular end-diastolic pressure were similar in the two groups. These data suggest that higher baseline beta-endorphin plasma levels may play a role in the decreased sensitivity to pain in patients with silent myocardial ischemia. In addition, different beta-endorphin levels can be associated with a different sensitivity to pain.