The authors have developed a new method for independent lung ventilation (ILV). After lung isolation with a double-lumen endotracheal tube, one ventilator with two subunits controls independent lung tidal volume (VT) and PEEP to each lung. A modified bird Mark 2 ventilator serves as a pneumatically powered timer activating two sets of parallel inspiratory-expiratory flow cartridges. Intermittent mandatory ventilation (IMV) with PEEP or controlled mechanical ventilation (CMV) with PEEP can be provided. This ventilator has been successfully used to treat patients with severe unilateral disease. Desirable qualities include simplicity of operation, availability of parts, and low cost.