The microscopic imaging of specific organelles has become a staple of the single-cell assay and has helped define the molecular regulation of many physiological processes. This definition has been made possible by utilizing different criteria to identify specific subpopulations of organelles. These criteria can be biochemical, immunological, or physiological, and in many cases, markers regulate fusion to the organelle they define (e.g., Rab-GTPase proteins). Single-cell imaging technology allows, within the context of drug delivery, an evaluation of the intracellular trafficking of both biological and synthetic macromolecules. However, it should be remembered that there are many limitations associated with this type of study and quantitation is not easy. The temporal dissection of novel and default trafficking of both macromolecular "drugs" and macromolecular drug delivery systems is possible. These methodologies are detailed herein.