The events during a sclerosant injection were controlled radiographically. Vistarine forte containing 21.5% of total iodine makes the distribution of fluid clearly visible, both opacifying and sclerosing. 1 ml of air precedes the injection of 0.5 ml of sclerosant. This has shown that the "air-block", as found in the syringe, is not exactly a cushion of air separating the vessel wall from contact with the circulating blood. The air is distributed like a collar of pearls along the vein walls. These bubbles of air remain visible for a long time in the varicose convultions and this tend to hinder contact between the sclerosant and the intima of the varicose vein. As the slides show, it is a well demarcated segment of the varicose vein which comes into effective contact with the sclerosant. It is precisely this segment which subsequently becomes sclerosed. The sclerosant seeks a centripetal pathway in all positions, lying standing and sitting. The therapeutic effect is the same, and is independent of the position of the patient at the time of the injection of sclerosant.