The pathogenesis of local skin necroses after intramuscular injection of various drugs such as phenylbutazone (Embolia cutis medicamentosa, Nicolau's syndrome) is not clear. In an attempt to simulate this clinical feature experiments were performed on the rabbit ear lobe. A 20% phenylbutazone solution was injected paraarterial, intraarterial and paraarterial after perforation of the vessel. The drug produced a violent inflammation with all kinds of application. The local inflammation induced by paraarterial injection resulted in a fine scarring. Both other kinds of application produced necroses or even perforations. The histological examinations in these cases revealed massive destructions of the inner arterial wall. In control-experiments necroses or perforations were nerve observed. From these data the following conclusions on the etiology of Nicolau's syndrome can be drawn: Phenylbutazone injected into the vascular or perivascular tissue causes an obligatory inflammation. After lesion of an artery complete destruction of the vessel followed by necrosis of the skin may occur. It seems obvious that this secondary effect can not completely be avoided.