A prospective, multiple observer ausculatory and phonocardiographic study of 100 patients with pericardial friction confirmed the dominant prevalence of triphasic pericardial rubs (56 percent of patients with sinus rhythm). In 9 of 33 patients with various biphasic rub patterns there was summation of the ventricular diastolic rub with the atrial systolic rub, concealing an additional 10 percent of potential triphasic friction. Fourteen of 15 monophasic rubs were audible or recordable only during ventricular systole. Rubs were best heard along the left sternal border in 84 percent of cases and tended to be louder during inspiration than during expiration; in 35 cases there was no respiratory predilection. Twenty-three rubs were palpable. Ten rubs occurred in patients with pericardial effusion, five of whom had tamponade. Extension of the neck did not have a dependable effect on rub intensity.