Abstract: The invention is a control valve for a nebulizer for inhalation therapy which stops the supply of mist except when the patient is actually inhaling. The preferred structure is a "T" shaped configuration with the lower end mounted atop the nebulizer and one end of the horizontal breath tube used as a mouthpiece. A shuttle cylinder with a check valve slides axially within the breath tube and includes a hole which aligns with the feed tube when the shuttle is at the end toward the patient. In that position the shuttle permits the mist to reach the patient through the shuttle. However, when the patient exhales, the shuttle moves to the opposite end of its travel and closes off the supply of mist while permitting the exhaled air to exit.