Fourteen patients with aortic valve endocarditis were evaluated. Twelve patients had vegetations detected by two-dimensional echocardiography and two were diagnosed anatomically. M-mode echocardiography was positive in eight patients. Two-dimensional echocardiography was superior to M-mode in determining size, shape, and mobility of vegetations. The following three morphologic types of vegetative lesions were seen on two-dimensional echocardiogram: globular polypoid masses (seven); irregular, elongated lesions with chaotic movement (four); and a cord-like structure (one). Serial two-dimensional echocardiograms performed after completion of antibiotic therapy in seven patients revealed no change in appearance in five and complete disappearance in two patients. Among the 12 patients with vegetations visualized on the two-dimensional echocardiogram, seven responded to medical therapy, four required aortic valve replacement, and one patient died. One of the patients who initially responded to medical therapy eventually required aortic valve replacement following a second episode of aortic endocarditis. In those patients with negative two-dimensional echocardiograms, the vegetations were 3 mm in diameter or less at surgery or autopsy. Vegetations that were visualized on two-dimensional echocardiography were found to be at least 5 mm in diameter at the time of operation. Two-dimensional echocardiography is a valuable noninvasive tool in the evaluation of patients with aortic valve endocarditis.