Free-flow electrophoresis is a powerful tool to separate subcellular vesicles such as early and late endosomes from plasma membranes. Using this technique, the intracellular distribution of poliovirus type 2 Sabin (PV2) and its derived subviral particles was analyzed upon infection of HeLa cells. Comparison of various infection conditions showed that maximally 30% of total cell associated PV2 was found in endosomal compartments with the remainder being associated with plasma membrane fractions; 2% of viral label was recovered from the cytoplasm in form of free virions. Sucrose gradient centrifugation analysis of the viral material recovered from the respective fractions revealed that intracellular virus was exclusively in its native conformation. This is in sharp contrast to human rhinovirus serotype 2 (HRV2), which is rapidly modified to RNA-free subviral particles upon accumulation in endosomes. The data suggest that productive poliovirus uncoating can occur at the plasma membrane whereas internalized virus is most probably aborted.