A new technique is described for selective lung ventilation of patients with predominantly unilateral pulmonary pathology. Separate ventilators were used to inflate each lung via a double lumen endobronchial tube and no attempt was made to synchronize them. In three of the four cases, there was considerable improvement in respiratory function and radiographic appearance. In no case was there any cardiovascular depression. The use of a new endobronchial tube, the "broncho-cath", suitable for this technique is also described.