Exposures to airborne nanosized particles (< 100 nm) have been experienced by humans throughout their evolutionary stages. Recently, the rapidly developing field of nanotechnology is likely to become yet another source for human exposures to nanosized particles - engineered nanoparticles (NPs) - by different routes, I.e., inhalation, ingestion, dermal, or even injection. Nanotechnology is defined as research and technology development at the atomic, molecular, or macromolecular levels, in the length scale of ～1 - 100 nm range. One of the many promising applications of engineered NPs is in the area of medicine, for example, targeted drug delivery as aerosols and to tissues which are difficult to reach. The discipline of nanomedicine has arisen to develop, test, and optimize these applications. However, the same properties that makes NP attractive for development in nanomedicine and for specific industrial processes could also prove deleterious when NP interact with cells. An emerging discipline - nanotoxicology, which can be defined as safety evaluation of engineered nanostructures and nanodevices - is gaining increased attention. Nanotoxicology research will not only provide information for risk assessment of NP based on data for hazard identification, dose-response relationships, and biokinetics, but will also help to advance further the field of nanomedicine by providing information to alter undesirable NP properties. Although potential adverse effects of engineered NP have not been systematically investigated, there are a number of studies in the area of inhalation toxicology and also human epidemiology from which some preliminary conclusions about effects of nanosized particles can be drawn. There are also some decades-old - mostly forgotten - studies with nanosized particles which shed light on the biokinetics of such particles once introduced into the organism. This presentation summarizes results of studies with nanosized particles with a focus on the respiratory tract and skin as portals of entry.
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