The duplex PCR assay was optimized for discriminating cow milk in goat cheese matrices to detect adulteration of cheese with cow milk. The PCR tests used in this screening were very sensitive, specific, and reproducible. Duplex PCR tests showed a minimum detection limit of 0.5% (vol/vol), indicating that the analytical assay unequivocally detected cow milk, even when it was present in small amounts (Figure 1). The detection limit is very similar to that described by Bottero et al. (2003) and Feligini et al. (2005). Other authors detected amounts of cow milk as low as 1% (Mašková and Paulíčková, 2006) and 0.1% (López-Calleja et al., 2005; Mafra et al., 2007). Although the PCR tests optimized in this study were able to detect amounts as small as 0.5% cow milk, it should be noted that amounts ≤1.0% of cow milk may well arise from involuntary cross-contamination during cheese manufacturing, if the dairy plant is not exclusively dedicated to goat cheese manufacture, or during the collection of milk from several farms that also produce cow milk (Mašková and Paulíčková, 2006).