Enterococci caused eleven of 20 cases (55%) of narcotic-associated endocarditis in Cleveland over a 54-month period. Acute staphylococcal endocarditis seen concurrently in this addict population displayed tricuspid valve involvement and septic pulmonary emboli, but enterococcal endocarditis was subacute, affected only aortic or mitral valves, and was not associated with septic pulmonary emboli. In contrast to enterococcal endocarditis in a nonaddict population, patients were younger and rarely had antecedent valvular disease or genitourinary abnormality. Staphylococcal tricuspid valve endocarditis was managed with relatively little difficulty in this addict population. Enterococcal infection, however, was complicated by severe cardiac failure that often required valvular prostheses, relapses due to continued use of narcotics, Candida superinfection, and nervous system complications, including cerebral emboli and mycotic aneurysms.