As the nanotechnology field continues to develop, assessing nanoparticle toxicity is very important for advancing nanoparticles for biomedical application. Here we report cytotoxicity of gold nanomaterial of different size and shape using MTT test, absorption spectroscopy and TEM. Spherical gold nanoparticles of different sizes are not inherently toxic to human skin cells, but gold nanorods are highly toxic due to the presence of CTAB as coating material. Due to toxicity of CTAB, and aggregation of gold nanomaterials in the presence of cell media, we have demonstrated that it is difficult to understand the cytotoxicity of gold nanomaterials individually. (c) 2008 Elsevier B.V. All rights reserved.