We studied 142 consecutively autopsied patients prospectively to determine the frequency and clinical importance of right-sided endocardial lesions in patients who had undergone flow-directed pulmonary-artery catheterization within one month of death. Of the 55 catheterized patients, 29 (53 per cent) had one or more right-sided endocardial lesions: 12 (22 per cent) had subendocardial hemorrhage, 11 (20 per cent) sterile thrombus, 2 (4 per cent) hemorrhage and thrombus, and 4 (7 per cent) infective endocarditis. Of 41 lesions seen in the 29 patients, 23 (56 per cent) were located on the pulmonic valve, 6 (15 per cent) on the tricuspid valve, 6 (15 per cent) in the right atrium, 4 (10 per cent) in the right ventricle, and 2 (5 per cent) in the main pulmonary artery. All four patients with infective endocarditis had had positive antemortem blood cultures while the catheter was in place, but in only one had the diagnosis of endocarditis been suspected clinically. The unusual locations of the infected vegetations (on the pulmonic valve in three and in the right atrium in one) and the similar location of the uninfected lesions suggest that the infective endocarditis was a consequence of catheter-induced endocardial damage with concurrent or subsequent bacteremia. Among the 87 non-catheterized patients, there were two subendocardial hemorrhages and one resolving right atrial thrombus. We conclude that endocardial damage from flow-directed pulmonary-artery catheterization is common and that right-sided infective endocarditis should be suspected in bacteremic catheterized patients.