A 60-year-old woman undergoing surgery died from endotoxic shock and DIC after receiving a 19-day-old unit of optimal additive red-cell concentrate found contaminated with Serratia liquefaciens. No source of contamination could be found. This normally free-living organism is usually of low pathogenicity. It is a very unusual contaminant of stored donated blood, although it appears to be on the increase. When transfused, blood contaminated with S. liquefaciens always causes severe morbidity and is associated with a high death rate. This is the fifth report in the English literature.