In 1988 we quantified the adherence of two Staphylococcus epidermidis strains to glutaraldehyde-fixed bovine pericardium and teflon. The pericardium was used with and without prior rinsing to remove the preservative formaldehyde. Bacterial adherence was not detected on non-rinsed pericardium, and it was significantly less on rinsed pericardium than on teflon (p < 0.001). In view of these results, we have since then implanted 31 pericardial bioprostheses without rinsing them in 29 patients with active bacterial endocarditis. Valve infection reoccurred in two patients (6.7%) and two patients developed early periprosthetic leaks in the absence of re-infection. No adverse clinical or biochemical findings attributable to residual aldehydes have been observed.