Wheat contamination in gluten-free foods (n = 26) purchased on Internet sites in Japan was investigated. A set of primers for the universal detection of plants was newly constructed to amplify the sequence of rbcL. The rbcL primers were demonstrated to produce a sufficient amount of amplification products from fifteen DNA samples of plants. The primer set Wtr01－5′ and Wtr10－3′ was applied to wheat detection following the official method for the wheat allergen in Japan. As a result, none of the twenty-three examined gluten-free foods was wheat-positive by PCR screening. For three foods, amplification products were insufficient with both the rbcL primer and Wtr primer sets. This may have been due to DNA fragmentation during their production. More gluten-free samples must be tested to estimate the wheat contamination risk.
