Over a 5-year period (1982-1986) 176 cases of infective endocarditis on prosthesis (IEP) were recorded in 40 cardiology departments. 65 p. 100 of the patients were male, and the mean age of the population was 51 years. Mechanical prostheses were involved in 57 p. 100 of the cases and bioprosthesis in 43 p. 100. There was a high proportion of initial indications for bacterial endocarditis (18 p. 100) and for reoperation on prosthesis (10 p. 100). IEP developed early in 40 cases and late in 139 cases; 19 (48 p. 100) of the early IEPs were staphylococcal, while 31 p. 100 of late IEPs were streptococcal (p less than 0.01). 143 patients were reoperated upon within less than 1 month in 41 p. 100 of the cases, with a pre-operative antibiotic therapy of less than 10 days in 39 p. 100. Reoperation was performed in stage IV or as an emergency in 45 p. 100 of the cases. Abscesses were three times more frequent with aortic prostheses than with mitral prostheses (58 p. 100 vs 20 p. 100, p less than 0.001). Vegetations were more frequent on mechanical prostheses than on bioprostheses (43 p. 100 vs 31 p. 100, NS). The operative mortality rate was 25 p. 100; the mortality rate of unoperated patients was even higher (31 p. 100). The survival rate in operated IEP was 51 p. 100 at 30 months, as against 46 p. 100 at 12 months in unoperated IEP.(ABSTRACT TRUNCATED AT 250 WORDS)