CONFERENCE PROCEEDING Proceedings of the PDA/FDA Adventitious Viruses in Biologics: Detection and Mitigation Strategies Workshop in Bethesda, MD, USA; December 1-3, 2010 Guest Editors: Arifa Khan (Bethesda, MD), Patricia Hughes (Bethesda, MD) and Michael Wiebe (San Francisco, CA) The detection of known and novel viruses is important for cell substrate and vaccine safety. A major challenge is detection of latent viruses such as endogenous retroviruses and oncogenic DNA viruses. We have evaluated activation of endogenous retroviruses in a Vero cell line using chemical induction and various conventional and emerging methods for virus detection and characterization. In addition, infectivity studies were done to determine whether any induced virus particles were replication competent. This approach may be used for enhancing vaccine safety by assessing the presence of potential chemically-inducible, latent viruses in cell substrates to be used for vaccine manufacture.