We have studied the subcellular localization of DV1 E and RSPs in the HeLa-prME cell line. By immuno-staining of fixed cells and fluorescence microscopy, we have shown that most of the E protein is localized in the ER compartment, where dengue glycoproteins are synthesized [1] . The fact that we did not detect any significant signal of E in ERGIC and Golgi apparatus could be explained by a very low amount of protein in these organelles. In these conditions, saturating signals in the ER would mask its detection in other compartments along the secretory pathway. The fluorescent microscopy results were in accordance with our electron microscopy data. Analysis of cell sections by transmission electron microscopy has revealed that E proteins in the ER are associated with both round particles and tubular structures. The tubules could either be intermediate forms of RSPs assembly or result from accumulation of prM and E proteins in the ER. Budding of virions from cellular membranes depends on assembly of viral structural proteins that generate pushing and/or pulling forces simultaneously to induce curvature of membranes, which is necessary for particle formation and membrane fission. It is possible that assembly of overexpressed prM and E proteins in the ER allows formation of long tubules but that the fission event is a limiting factor. The secretion pathway was also investigated by temperature block or pharmacological experiments. Incubation at either 15uC, to stop traffic between the intermediate compartment and the cis-Golgi, or at 20uC, to block exit from the trans-Golgi network, or BFA treatment, to block the exit from ER, significantly reduced secretion of RSPs. These results demonstrate that RSPs traffic through ER, ERGIC and Golgi compartments before being secreted out of the cell.