The hazard of transfusion of stored blood contaminated with an organism which grows well at refrigeration temperature is illustrated by the description in detail of a single fatal case, as well as a tabular summary of 41 cases collected from the literature and personal communication. Gram negative bacilli produced the most frequent and most severe reactions, with a mortality of 65%, and this is correlated with their greater production of pyrogenic toxins. The nature of the reaction is descr., with emphasis on hypotension coupled with cutaneous vasodilatation. The shock phase is resistant to treatment. Recognition and prevention of bacterial contamination of stored blood are discussed.