Jet nebulization is a common technique by which gene therapies can be delivered to the lungs, however current research has shown a reduction in activity and effectiveness of these treatments when not complexed with cationic agents. To date, a systematic investigation of chemical and mechanical degradation pathways has yet to be undertaken to identify the proximate cause of DNA instability. The purpose of this paper is to identify the dominant chemical and/or mechanical mechanism(s) by which DNA degrades when subjected to jet nebulization. Investigation of multiple degradation pathways revealed hydrodynamic shear to be primarily responsible for the observed loss in DNA integrity. Complexation of DNA with cationic agents polyethyleneimine or poly-L-lysine to DNA was sufficient to overcome these mechanical forces via a reduction in applied hydrodynamic forces. (C) 2004 Elsevier Ltd. All rights reserved.