Semiconductor nanoparticles in the quantum confinement regime used as biolabels present many advantages over the other chemical species used as fluorophores. They are composed of 2000-6000 atoms rendering a far greater photostability and allowing for long time bioimaging experiments. In this work we present a synthetic route for the obtention of large quantities of highly fluorescent CdSe and CdTe/CdS core-shell nanocrystals based on aqueous colloidal chemistry. The methodologies were optimized and the systems were characterized by optical spectroscopy, transmission electronic microscopy and X-Ray diffractometry. The fluorescent biolabels were tested in live macrophages. (C) 2008 Elsevier B. V. All rights reserved.