Scientists fear that metal and metal oxide nanoparticles may be potentially hazardous due to the special catalytic activity arising as a result of the properties at the nano interface. Additionally, their decomposition may lead to an increase in intracellular ion concentration and interfere with cell metabolism. A very specific problem in dealing with the toxicological evaluation of nanomaterials, and in particular with metal oxide nanoparticles, is the difficulty of localising and quantifying them in cells and organs. To this end, the EU-funded HINAMOX project synthesised specifically labelled nanoparticles for use in in vitro cell assays to trace their biodistribution. Radiolabelled metal and metal oxide nanoparticles were generated that could be traced by positron emission tomography (PET) and single photon emission computed tomography (SPECT). Fluorescently labelled particles were also designed and used for uptake studies in vitro. The intracellular fate of these particles is dependent on their characteristics, surface chemistry, and interaction with proteins and other biologically relevant molecules. To study nanoparticle processing within cells, partners applied confocal Raman microscopy, transmission electron microscopy (TEM), ion beam microscopy (IBM) and confocal laser scanning microscopy. In vitro culture of nanoparticles with cells revealed that internalisation required at least 12 hours. Uptake was hindered by the presence of protein coronas on the nanoparticle surface and confocal microscopy of fluorescently labelled nanoparticles showed an internalisation pattern that correlated with endosome/lysosome uptake. Scientists also studied the cytotoxicity, immunological impact and oxidative stress effect of metal nanoparticles on macrophages, alveolar epithelial type two (ATII) cells and lung epithelial cells. This analysis was of high physiological relevance as lung inhalation constitutes the most likely route of nanoparticle exposure. In vivo biodistribution PET analysis following intravenous administration of nanoparticles unveiled a strong size dependency of the distribution and accumulation of nanoparticles in all organs. However, a negligible accumulation of nanoparticles was observed in the brain irrespective of size. The results of the HINAMOX study, combined with field measurements to assess nanoparticle emission during powder production, attest to health hazards posed by these novel materials. The outcomes of the study should provide a basis for the formulation of new health and safety procedures to minimise exposure to nanoparticles.