It should be noted that the frequency of amplification inhibition not only relates to the nature of the sample tested, but is also intrinsically linked with the technical protocols used for the extraction and amplification of nucleic acids. In our experience, no major differences were observed when different silica column-or magnetic beads-based extraction techniques, or different commercialized PCR or RT-PCR kits, were tested (data not shown). However, a detailed analysis may reveal that specific techniques give better results when used for testing specific samples. We suggest that, in the future, phage-based internal controls may constitute cost-effective tools with which to measure the frequency of amplification inhibition in specific samples. Estimation of this parameter may become a major criterion for the evaluation of extraction (and to a lesser extent amplification) techniques.