Primary idiosyncrasia against dextran does really exist and is to be taken into account. It may even be more frequent than is usually accepted because in many cases an other cause than the infusion may be obvious. The shock develops at the first milliliters of the infusion. When dextran is to be administered for the first time, a doctor is to be present and all equipment for resuscitation must be available. For any reaction occurring during the infusion, the dextran must be withdrawn.