The authors have adjusted a jet nebulizer to a mechanical ventilator (Servo Ventilator, Siemens) to deliver an aerosol to rats. They aimed to clarify whether a modified jet nebulizer generating particles with a mass median aerodynamic diameter of 2 microm would be effective and safe in intubated ventilated rats. Fluorescent microspheres (diameter: 1.0 microm) were aerosolized to verify qualitatively and quantitatively intrapulmonary deposition. Particle deposition fraction was 3.8% (1.3%) of the delivered dose (median [interquartile range]). There was no evidence for any adverse event as assessed from heart rate, mean arterial pressure, PaO2 and PaCO2 before, during, and after nebulization. No pulmonary tissue trauma was detected histologically.