Evidence that patients with rheumatic heart disease were not receiving adequate prophylaxis led to an investigation of the reason for this neglect. A series of 101 patients with rheumatic heart disease or past rheumatic fever were studied, first with regard to the severity of their condition and second with regard to the measures they were taking to prevent recurrences. No evidence was found to indicate that either the patient's age or the severity of his heart disease influenced his observance of a program of prophylaxis. The most definite factor increasing the likelihood of such observance was his exposure to the influences of a teaching hospital. In a few instances private physicians seemed to be unaware that a free supply of penicillin was available. Both physicians and patients need to be educated about the need for prophylaxis and the means available.