Apparatus and method is disclosed for vaporizing a liquid anesthesia agent in a carrier gas for delivery to a patient such that the apparatus automatically establishes, monitors, and maintains a predetermined concentration level of the anesthesia agent in the carrier gas. The apparatus has an inlet and an outlet with a vaporization chamber therebetween, and a pump for dispensing small quantities of liquid anesthesia agent into the vaporization chamber. A first sensor senses the condition of the carrier gas upstream from the vaporization chamber and a second sensor senses the condition of the carrier gas/vaporized agent downstream from the vaporization chamber. A computer control system responsive to the sensors is configured to determine the concentration level of the agent delivered to the patient and to automatically increase or decrease the rate at which the pump is actuated to maintain the concentration level at the predetermined level.