A new technique for vascular embolization using two Gianturco steel coils is described. The authors used a "coil-in-coil" technique to embolize the arteries of 12 dogs. In this technique a large coil is introduced into the artery followed by a smaller coil, which is delivered with a special introducer into the lumen of the first coil. Two coils can therefore be introduced into a shorter length of vessel. This method was as effective as "packing" the vessel with two coils in a row. The coil-in-coil technique is especially advantageous for use in infants and children with short, anomalous vessels, minimizing the risk of coil dislodgment into normal peripheral vessels.