One of the major challenges in the initial treatment of critically ill or injured patients is the establishment of a well functioning intravenous access. This can be very difficult in patients with circulatory collapse, and almost impossible in infants. Central venous cannulation is time-consuming and requires skill. Nor can intratracheal and rectal administration of drugs and fluids fully replace the intravascular route. In such situations the old but forgotten technique of intraosseous infusion represents an elegant and easy way of gaining rapid intravascular access. The method is simple, safe and almost foolproof, and can easily be performed under field conditions, e.g. by paramedical personnel. Very few contra indications exist, and the success rate even by untrained personnel is high. In this review the physiological aspects and the technique itself is discussed and illustrated by case reports.