Atrium, ventricle, aorta, lung, kidney, and rectum were removed at autopsy from 85 consecutive elderly patients (aged 80 years or older) and examined for amyloid with Congo red. All tissues containing amyloid were counterstained with an antiserum specific for amyloid fibril protein ASc₁ and studied by immunofluorescence. Three distinct forms of amyloid were found: (1) all patients had senile aortic amyloid; (2) 78 percent of patients had isolated atrial amyloid; and (3) 25 percent of patients had senile cardiac amyloid of the ASc₁ type. The cardiac amyloid deposits were small and widely scattered in more than 80 percent of patients with isolated atrial amyloid and in more than 50 percent of patients with ASc₁-type amyloid. Of 21 patients with ASc₁ amyloid, 19 had extracardiac involvement (lung in 81 percent of cases and rectum in 57 percent of cases). The kidney was not involved in any patient. The mean heart weight, frequency of atrial fibrillation, percentage of patients with heart failure, and frequency of myocardial infarction were increased in patients with cardiac amyloid, but these differences failed to reach statistical significance. There was no difference in the mean left ventricular wall thickness or degree of coronary atherosclerosis.