Twelve patients suffering from subclavian steal syndrome of various severity due to either proximal subclavian stenoses (10 cases) or subclavian occlusion (2 cases) were treated with percutaneous transluminal angioplasty (PTA). Olbert's dilatation catheters were used. The occlusions could neither be recanalized by the transfemoral nor transaxillary approach. In one right-sided subclavian stenosis an additional distal subclavian occlusion prevented proper placement of the catheter. All the other patients were treated successfully with no re-occlusion during a follow-up period of 1 to 7 months. In one patient, a transient embolic occlusion of the finger arteries was seen following post-interventional repeat angiography. Before, during and after PTA, continuous ultrasound monitoring of the homolateral vertebral flow patterns revealed an unexpected "delay" phenomenon. Despite sufficient recanalization of the proximal subclavian artery, the flow direction within the vertebral artery did not immediately change to antegrade but rather did so gradually within 20 s up to several minutes. This delay of flow-reversal is thought to serve as a protective mechanism against cerebral embolism during, and shortly after PTA of the subclavian artery. Relying on Doppler ultrasound findings, a staging of the subclavian steal is proposed in order to allow adequate selection of patients for PTA.