The invention relates to a novel method of administration, and device employed in the method, for administering a treatment species to the lungs of a recipient patient. The method involves introducing the device of the invention to the venous system of the patient, the size of the treatment species being such that, upon introduction to the venous system of the patient, the device will impact in a region of a lung capillary of the patient. The treatment species gains access to the lung and/or lung epithelia due to proteases associated with the treatments species. The application of the method to the treatment of cystic fibrosis is also claimed.