AbstractInadvertent hypothermia due to massive infusion of stored blood can be prevented by pretransfusion warming. One approach is the heating of individual packs by means of electromagnetic conduction, which is a method safely used over the last 25 years. The prototype instrument, which has now been re‐engineered, can effectively raise the temperature of a unit of blood to approximately 33°C in less than 3 minutes. Using this new model, we found, in vitro, a modest increase in free plasma haemoglobin, but this was not accompanied by any change in potassium or lactic dehydrogenase levels and the mean red cell fragility was unaltered. In vivo, the survival of autologous red cells that had been stored for 33 days and then infused as a concentrate, having a mean haematocrit of 0.60, was measured at 24 hours and 21 days. Each donor acted as his own control. In paired studies, pretransfusion radiofrequency heating was shown to have no deleterious effect when compared to measurements using the unwarmed blood pack. It is concluded that this method can be recommended as safe. © 1992 Wiley‐Liss