Between 1977 and 1992, 30 consecutive episodes of infective endocarditis in 28 patients involving pericardial bioprostheses were diagnosed and treated in our hospital. Eleven (37%) were early pericardial valve endocarditis occurring in the first 60 days following valve surgery, and 19 (63%) were late endocarditis. In both the early and late groups, more aortic that mitral valves were affected (19/30). The most frequent pathogen in the early cases was staphylococcus, (S. epidermidis in five cases, S. aureus in one). The most frequent pathogen among late cases was streptococcus: (St. viridans in four, St. faecalis in two, St. bovis in one). In four cases (13%) no pathogen was isolated. Twelve patients received antibiotic treatment alone, six specific for the pathogen and other six only arbitrarily chosen regimen. All patients were cured in the former and all patients died in the latter group (four with negative blood cultures and two in whom identification of the pathogen was delayed-Proteus mirabillis in one case and Brucella mellitensis in the other). Valve replacement during the infective endocarditis episode was necessary in 18 cases, either because of failure of the antibiotic treatment or because of heart failure secondary to prosthetic malfunction. Peri-annular abscess was present in five cases. Surgical mortality was 22.2% (4/18). In all, 11 patients (39%) died during the active stage of infective endocarditis. The most frequent cause of death was heart failure (45.5%). All four patients with negative blood cultures died. The most advisable strategy for treating bacterial endocarditis of pericardial bioprostheses is a combination of antibiotic therapy and early surgery, especially in cases of staphylococcus endocarditis.(ABSTRACT TRUNCATED AT 250 WORDS)