Human rhinoviruses (HRVs) are valuable tools in the investigation of early viral infection steps due to their far reaching (although still incomplete) characterization. During endocytosis, native virions first loose one of the four capsid proteins (VP4); corresponding particles sediment at 135S and were termed subviral A particles. Subsequently, the viral RNA genome leaves the viral shell giving rise to empty capsids. In continuation of our previous work with HRV serotype 2 (HRV2) intermediate subviral particles, in which we were able to discriminate by CE even between two intermediates (AI and AII) of virus uncoating, we further concentrated on the characterization of AI particles with the electrophoretic mobility of around -17.2 x 10-9 m2/Vs at 20 degrees C. In the course of our present work we related these particles to virions as previously described at the subviral A stage of uncoating (and as such sedimenting at 135S) by determination of their protein and RNA contentin comparison to native virions AI particles did not include VP4, however, still 93% of their initial RNA content. Binding of an mAb specific for subviral particles demonstrated antigenic rearrangements on the capsid surface at the AI stage. Furthermore, we investigated possible factors stabilizing intermediates of virus uncoating. We could exclude the influence of the previously suspected so-called contaminant of virus preparation on HRV2 subviral particle formation. Instead, we regarded other factors being part of the virus preparation system and found a dependence of AI particle formation on the presence of divalent cations.