A method of treating a disease involving surfactant deficiency or dysfunction in a patient's lungs is disclosed comprising the steps of providing a liquid lung surfactant composition; aerosolizing the lung surfactant composition with a vibrating aperture-type aerosol generator to form a surfactant aerosol; and introducing the surfactant aerosol into the gas flow within a circuit of a pressure-assisted breathing system coupled to the patient's respiratory system, whereby a therapeutically effective amount of said surfactant is delivered to the patient's lungs. Apparatus is also disclosed that increases the efficiency of delivery of aerosolized medicaments such as aerosolized lung surfactant.