The object of this study was to evaluate in vitro the influence of various ventilatory parameters on the delivery of synchronized nebulization of terbutaline during mechanical ventilation and to determine a semiempirical model to control the quantity of aerosol delivered into the patient's lung. An ATOMISOR NL9 M jet nebulizer (La Diffusion Technique Francaise, France) was filled with terbutaline (Bricanyl, Astra-Zeneca, Sweden) and connected to the inspiratory line of a Horus ventilator (Taema, France). Nebulization was synchronized with the inspiratory phase. We assessed at the end of the endotracheal tube the quantity of terbutaline (terbutaline mass output) and the volume median diameter (VMD) by diffraction-laser method. There was a negative correlation between terbutaline mass output and inspiratory air flow ( r =-0.95, p <0.0001) and between VMD and inspiratory air flow ( r =-0.96, p <0.0001). Moreover, positive end-expiratory pressure levels between 0 cm and 8 cm of water did not significantly change the terbutaline output mass ( p =0.22). Total nebulization time and terbutaline mass output calculated by the mathematical model showed good agreement with experimental data. In conclusion, our semiempirical model allows calculation of the duration of the nebulization required to deliver a given mass of terbutaline into patient lungs.