Sixty-four patients with one or more bioprostheses were reoperated between 1970 and 1982. Reoperation was performed for degenerative lesions in cases (48%), for aseptic periprosthetic leaks in 18 cases (28%), for infectious lesions in 13 cases (21%) and for thrombosis in 2 cases (3%). Degenerative and infectious lesions were commoner in aortic bioprostheses whilst periprosthetic leaks were commoner in mitral bioprostheses. The average interval between operations was 38 months. This was shorter in patients reoperated for mechanical problems (6 months) than those with infections (28 months) or degenerative (5 years) complications. At reoperation 14 prostheses were reinserted and 50 were replaced. The global hospital mortality was 21% (14 deaths). The mortality was related to the surgical indication: mechanical lesions (11%), degenerative lesions (16%), infectious endocarditis (38%), thrombosis (100%). The mortality rate also varied with time (36% during the period 1970-1978 and 18% during the period 1979-1982). This improvement was related to two factors: the use of cardioplegic solutions for myocardial protection and earlier recognition of surgical indications before the onset of irreversible haemodynamic complications. When choosing a valvular prosthesis, the mortality of reoperation for degenerative changes is the only disadvantage of the bioprosthesis which is silent, rarely complicated by thromboembolism and which does not require anticoagulant therapy for life. The mortality has decreased with time and will continue to fall if the indications for reoperation are based on stethacoustic, electrical, radiological and echocardiographic criteria of valvular dysfunction and not on the presence of overt cardiac failure as is still often the case.