The present invention provides an improved means of treating tracheobronchitis, bronchiectasis and pneumonia in the nosocomial patient, preferably with aerosolized anti gram-positive and anti-gram negative antibiotics administered in combination or in seriatim in reliably sufficient amounts for therapeutic effect. In one aspect, the invention assures this result when aerosol is delivered into the ventilator circuit. In one embodiment the result is achieved mechanically. In another embodiment, the result is achieved by aerosol formulation. In another aspect, the invention assures the result when aerosol is delivered directly to the airways distal of the ventilator circuit. The treatment means eliminates the dosage variability that ventilator systems engender when aerosols are introduced via the ventilator circuit. The treatment means also concentrates the therapeutic agent specifically at affected sites in the lung such that therapeutic levels of administrated drug are achieved without significant systemic exposure of the patient to the drug. The invention further provides a dose control device to govern this specialized regimen.