The colloidal properties of delivery systems currently being developed for nonviral gene therapy are extremely important. The physical stability of these systems on the shelf, as well as in the biological milieu, is mostly based on their size and interfacial properties. The size and surface charge of these systems can also have dramatic effects on their biological activity (1 –4 ). With these facts in mind, it is apparent that adequate characterization of these properties is necessary for the development of any synthetic gene delivery system.
