To achieve synchronized differential pulmonary ventilation, an Ohio 560 ventilator was modified through separation of the outputs of the deep breath bellows and the tidal volume bellows and providing independent volume, flow rate, PEEP, oxygen-humidification, and alarm systems. The described ventilator modification is simple, inexpensive, and does not alter the performance characteristics of the original unmodified ventilator. Differential lung ventilation may be more easily achieved with this modified ventilator than with the simultaneous use of two ventilators or external electronic synchronizers.