High frequency ventilation techniques are accepted for upper airway and intrathoracic surgery under general anesthesia. Good oxygenation and ventilation are acheived with good airway control and operative conditions. However, the jet ventilating system is of an open-character with mandatory use of intravenous anesthesia. The present study was done to administer inhalation anesthetics(halothane)during high frequency ventilation. The high frequency injector was adapted to an angiocartheter wit a swivel connector, while the entrainment orifice of the side port was connected to the anesthesia circuit to facilitiate the administration of inhalation anesthetics. Variables thought to be important in determing the inspiratory peak halothane concentration and diluting inspiratory oxygen concentration for estimation of gaseous influx from the anesthesia circuit were evaluated in an experimental lung model Changing the halothane concentration of the vaporise(1,3,5%), inspiratory: expiratory(I:E) ratio(0.2:0.2, 0.2:0.4, 0.2:0.6, 0.2:0.8, 0.2:1.0 sec.), driving gas pressure(DGP)(10,30,50 psi), the inspiratory peak halothane and oxygen concentration were measured. The results were analyzed to predict the association and relationship of the inspiratory peak halothane and oxygen concentration with each variable. Partial coefficient of halothane concentration of the vaporizer, I:E ratio, DGP were -0.7224, 0.3724, 0.3386 and R squares were 0.5219, 0.6605, 0.7752 to the inspiratory peak halothane concentration. Partial coefficient of I:E ratio, DGP were-0.9386, 0.1138 and R squares were 0.8809, 0.8939 to the inspiratory oxygen concentration. Halothane concentration of the vaporizer was the most associated factor to the inspiratory peak halothane concentration and I:E ratio to the inspiratory oxygen concentration. Clinically, if DGP and I:E ratio are determined, the halothane concentration of the vaporizer will be the predictor of the inspiratory halothane concentration. But in a certain condition, the inspiratory peak halothane concentration could not be achieved to a proper level for maintaing anesthesia by this experimental model. In conclusion, most of the high frequency jet systems used clinically are of the open character allowing entrainment of additional gases and difficult to apply if volitile agents are to be used. Special predictable vaporizers have to be developed to apply volitile agents in any situation of I:E ratio and DGP by this method of administering inhalation agents during high frequency jet ventilation.