Reovirus is internalized after interaction of the outer proteins μ1, σ1 and σ3 with the host cell. Proteolysis of σ3 and cleavage of μ1 (into δ and φ) eventually leads to the formation of a more infectious subviral particle named “ISVP”. The infectious entry of viruses, but not of ISVPs, can be blocked using various entry inhibitors and therefore, suggests that there is a threshold of σ3 digestion required to allow particle to bypass entry blockers. By combining protease and detergent to the digestion of virions, data from this work showed distinct particles generated along the transition pathway. In addition, studies involving flow cytometry and specific antibodies (anti-μ1) showed that between virus and ISVP there is a gradual yet heterogeneous particle proteolysis that is directly related to the virus infectivity. The findings and approaches taken for this thesis work can possibly be extended for studying other non-enveloped viruses. Moreover, it may help to shed some light on the development of safe and effective oncolytic agents.