Vaccines are ... under investigation for the possible side effects they can cause. In order to supply new information, an electron-microscopy investigation method was applied to the study of vaccines, aimed at verifying the presence of solid contaminants by means of an Environmental Scanning Electron Microscope equipped with an X-ray microprobe. The results of this new investigation show the presence of micro- and nanosized particulate matter composed of inorganic elements in vaccines' samples which is not declared among the components and whose unduly presence is, for the time being, inexplicable. A considerable part of those particulate contaminants have already been verified in other matrices and reported in literature as non biodegradable and non biocompatible. The evidence collected is suggestive of some hypotheses correlated to diseases that are mentioned and briefly discussed. Not all the vaccines analyzed contain the same contamination, though the same vaccine belonging to different batches and, in some cases, coming from different countries can contain a similar contamination Vaccines by Glaxo - Infarix, Typherix and Priorix - contain Tungsten. Tungsten was also identified in [the vaccines] Menjugate Kit by Novartis, and Prevenar, Meningitec by Pfizer and Meningitec by Wyeth. Feligen, the only veterinary vaccine tested, proved to be the only sample free from inorganic contamination.