The efficiency of removing inhibitors in patient samples may be related to the intrinsic properties of the method used to extract the RNA [15] . In this study we compared four commercial RNA extraction systems efficiencies for RNA isolation and removal of inhibitors in stool samples. The extraction systems were: QIAamp Viral RNA Mini Kit: manual extraction using silica columns (QIAGEN Inc, Valencia, CA, USA); MagNA Pure LC2.0 Automatic extractor with MagNA Pure LC Total Nucleic Acid Isolation Kit-High Performance: automatic RNA extraction using magnetic beads (Roche Diagnostics, IN, USA); KingFisher (Thermo Electron Corporation, Waltham, MA, USA) semi-automatic extraction using magnetic beads of Ambion MagMAX Viral RNA Isolation kit (Ambion, Inc, Austin, Tx, USA); NucliSENS easyMag (bioMerieux, Marcy l'Etoile, France): semi-automatic extractor using magnetic beads of easyMag extraction kit. In addition, the effectiveness of MS2 as an exogenous template control for measuring inhibitors co-extracted with RNA from stool suspen-sions and its relevance for validation of enterovirus diagnostic rRT-PCR suspensions is discussed.