The precautionary principle has boomed in the French public health sector through blood transfusion. There has been, however, no perambulatory reflection on the definition, objectives, methods of application or consequences of this principle. The question of the pertinence of its application remains unanswered. This study, based on interviews with blood transfusion practitioners, aims to establish their perceptions of the precautionary principle's application in this specific field and of its consequences in terms of risk management and patients' rights. The pros and cons of this application are analysed based on these perceptions. According to our analysis, the precautionary principle seems to be born of confusion. It is seen more as a way to protect decision makers than patients and, if taken to extremes, could prejudice medical logic. Nevertheless, it also brings measures which renew and encourage evolution in transfusion risk management.