Although rare, Serratia marcescens endocarditis has been reported in patients after surgical placement of a Starr-Edwards valve. Of four previously reported patients only one survived. In the present case report, bacteriologic cure was achieved by antimicrobial therapy alone. Artificial valve endocarditis of this type may be managed without resorting to valve replacement if hemodynamic deterioration does not occur and if an antimicrobial agent can be identified which will kill the organism in vitro in levels that can be achieved clinically. Carbenicillin is potentially useful for treating serious Serratia infections. © 1973 Southern Medical Association.