The Oslo Ischemia Study was initiated between 1972 and 1975 in 2,014 men (age, 40-59 years), with the aim of detecting previously unknown and unsuspected coronary heart disease. Of the men who were eligible, 86% participated and were apparently free from cardiovascular disorders. Following a positive symptom-limiting bicycle test, 109 of the men underwent diagnostic coronary angiography and 105 were evaluable; the angiograms were normal in 36 and pathologic in 69. Nineteen of the men with pathologic angiograms had mild angina on the exercise test, while 50 (72%; 2.5% of total study population) remained completely asymptomatic. During a mean follow up of 15 years, 14 of the 50 completely asymptomatic men died (12 suddenly, 1 of whom had angina pectoris for 5 years). Eighteen of the surviving 36 men remained completely asymptomatic and free from signs of coronary artery disease, other than exercise-induced ST-segment depression. One man had ECG signs of a previous myocardial infarction, on the annual follow up; chest pain as a first presenting symptom was observed in a further 17 of 36 survivors. Repeat angiography was performed in 22 men who experienced either chest pain or worsening symptoms following exercise test; of these, 14 underwent coronary bypass surgery and are still alive. The data appear to refute a ‘wait-and-see’ policy among subjects with asymptomatic cardiac ischemia. It is concluded that medical or surgical intervention can affect prognosis in the asymptomatic or mildly symptomatic phase of coronary artery disease. Further trials are in progress to evaluate if prognosis can be improved by effective anti-ischemic intervention.