Semiconductor quantum dots are a promising class of materials in the labeling of biological systems. In the present study we show the marking pattern of Trypanosoma cruzi (T. cruzi) live parasites using PEGylated CdS/Cd(OH)(2) fluorescent nanocrystals. The analysis obtained by confocal fluorescence microscopy and transmission electron microscopy indicates that only the endocytic paths of parasites were labeled. The parasites were alive after the incubation with the CdS/Cd(OH)(2)-PEG suspension. Labeling the T. cruzi with quantum dots can help to better understand the endocytosis process and also the cellular differentiation. (c) 2008 Elsevier B.V. All rights reserved.