It has previously been shown that trypsinized triple-layered particles of rotavirus induce destabilization of liposomes and membrane vesicles in the absence of Ca2+, a condition which leads to solubilization of the outer capsid proteins of the virus. In this work, we have studied the relationship between outer capsid solubilization and permeabilization of membrane vesicles, monitoring particle and vesicle size simultaneously by changes in light scattering. Permeabilization of intact cells induced by solubilized outer capsid proteins was monitored by following the rate of entry of ethidium bromide into the cells. Solubilized outer capsid proteins separated from double-layered particles induced vesicle permeabilization. Solubilization of the outer capsid preceded and was required for vesicle or cell permeabilization. Membrane damage induced by rotaviral outer proteins was not repaired upon addition of 1 mM Ca2+ to the medium. Rotavirus infection and cell permeabilization were correlated in six different cell lines tested. This phenomenon might be related to the mechanism of virus entry into the cell. We propose a new model for rotavirus internalization based on the permeabilizing ability of outer capsid proteins and the cycling of trapped calcium in the endosomal compartment.