Six cases of chronic endocarditis (more than 1 year duration) have been extracted from a series of 72 cases of endocarditis (delayed in 49) associated with intracardiac prosthesis observed over a 15-year period. In these 6 cases endocarditis developed 6 months to 2 years after valve replacement. The prosthetic material included 3 Starr-Edward's valves, 2 Hancock's valves and 1 intracardiac patch. The micro-organism isolated were Streptococcus in 3 cases, Serratia and Corynebacterium in 1 case each. The 18-month to 5-year course of the disease was marked by 2 to 5 relapses separated by long periods of apyrexia. The most significant complications were dysimmune syndrome (5 cases), embolic accidents (2 cases) and prosthesis disinsertion (4 cases). Five patients benefited from antibiotic therapy; 4 were operated upon with recurrent disinsertion in 2 cases. Two patients died, one of repeated disinsertion, the other of myocardial dysfunction. Bacteriostatic antibiotics were administered continuously to 3 patients whose endocarditis persisted or relapsed, with satisfactory results in two cases followed-up for more than 2 years.