The flagellar attachment zone (FAZ) is an adhesion region of Trypanosoma cruzi epimastigote forms where the flagellum emerges from the flagellar pocket and remains attached to the cell body. This region shows a junctional complex which is formed by a linear series of apposed macular structures that are separated by amorphous material and clusters of intramembranous particles. Two protein groups appear to be important in the FAZ region: a membrane glycoprotein of 72 kDa and several high molecular weight proteins. To gain a better understanding of the FAZ region, we compared wild-type Y strain T cruzi epimastigotes with a mutant cell in which the 72-kDa surface glycoprotein (Gp72), involved in cell body-flagellum adhesion, had been deleted by target gene replacement. Using immunofluorescence confocal microscopy and electron microscopy techniques to analyze the FAZ region the results suggest that, in the absence of Gp72, other proteins involved in the formation of FAZ remain concentrated in the flagellar pocket region. The analysis of a 3-D reconstruction model of wild-type epimastigotes showed that the endoplasmic reticulum and mitochondrion are in intimate association with FAZ, in contrast to the null mutant cells where the endoplasmic reticulum was not visualized. (c) 2005 Elsevier Inc. All rights reserved.