Dear MaryAnn, Whatever the source might be, the tech. will never belive it might be an artefact caused by testing or sampling procedures, and production will always belive that it came from sampling or testing. Both standpoints might be true, but with no evidence in any direction there is no possibility to rule out anything. You should try to find the contamination source, which might prove to be very difficult if it was only a temporary condition. However in parallel you should act, as if it were a contmination of the sample - take the possible meassures to reduce any possible bioburden. Kind regards Winfried Rapatz [log in to unmask] The opinion exppressed here represents the opinions of the author and do not necessarily represent the opinions of those who hold other opinions. (A.I.R. Vol. III, No. 1 January/February 1997, p2) ------------------ The PMFList (http://microbiol.org/pmf.htm) is operated from The Microbiology Network (http://microbiol.org) and supported by our sponsors (http://microbiol.org/sponsor.htm) as a service to the scientific community.