SummaryThe clinical features of a case of bacterial endocarditis superimposed on a congenital ventricular septum defect in a 54 year old man are presented.Aclinobacillus actinomycetemcomitanswas repeatedly isolated from the blood and the patient was successfully treated with penicillin and streptomycin. Our observation is the second such infection reported in detail from the European continent.Other published observations of endocarditis due to this organism, together with the bacteriologic characteristics of the bacterium are biefly discussed.