A critical review of the biological and medical effects of one dimensional nanoparticles is presented. The review focuses on the toxicity of carbon nanotubes - a subject under strong debate and discusses briefly the most important concepts. It is tentatively suggested that the huge aspect ratio and the high Young modulus of carbon nanotubes are playing an important role in the biological, medical, and toxicological aspects of carbon nanotubes despite their low intrinsic biochemical activity. The most suitable biomedical model for the biological and medical effects of carbon nanotubes is described by the so-called impaling mode which appears to be qualitatively consistent with partial phagocytosis. Published by Elsevier B.V.