Over the past 15 years, nucleic acid amplification techniques (NAT), also referred to as polymerase chain reaction (PCR), have played an increasingly important role in the characterisation and evaluation of biosafety for human biological therapies. Adventitious agents are of particular interest, as they pose a significant safety risk if present in vaccines or other biological therapeutics. Adventitious agents may contaminate cell lines from a number of sources including: (A) the individual from whom the cell line is derived; (B) media and tissue culture reagents containing products of animal origin; (C) human operators or others who may have contaminated the cells during handling under non-GMP conditions. Therefore, all materials, cell lines, primary cells, and tissue products used for therapeutic purposes require testing for a number of adventitious agents. The viruses to be assessed depend upon origin of the cell line and raw material used in manufacture1-16.