This almost exhaustive overview on the risk assessment of carbon nanotubes and on their potential beneficial use in the biomedical field, shows that the results of the experiments performed up to date on the toxicity of these C-nanoparticles are still not universal and need to be viewed as the basis for future investigations. However, some emerging concepts of nano toxicology can be identified from these data. Toxicity of C-nanotubes depends on several different factors, some belonging to CNT properties such as: size, shape, surface characteristics, amount of the substances present in the particles preparations (carbonaceous material, graphite particles, amorphous carbon), degree of functionalisation, degree of solubilisation, length of CNTs, degree and kind of agglomeration, catalyst metal; some to the biological environment: cell line, tissue type, animal species, route of administration, type of assay used for the measurement of cell viability (in some cases it has been demonstrated that CNTs can interfere with the dye resulting in false positive and/or negative results), etc. Furthermore, the physical form of carbon, such as the molecular structure and topology has been found to be essential for assessing the toxicity of any carbonaceous material. It has been demonstrated that the degree of solubility and dispersion of CNTs can completely change the behaviour of CNTs when in contact with cells. 18 The more hydrophobic pristine CNTs have been shown to be less toxic than the oxidized CNTs. The increased toxicity of oxidized CNTs being explained because they are better dispersed in aqueous solution and therefore can reach higher concentrations of free CNT at similar weight per volume values. 1