A growing body of evidence suggests that a majority of people with celiac disease and on a gluten-free diet can safely consume pure oats in moderate amounts; however, previous studies have indicated that the commercial oat supply in other countries, and in Canada to some extent, is contaminated with other grains. This study has confirmed that the commercial oat supply in Canada is heavily contaminated with gluten from other grains. Approximately 88% of the oat samples (n = 133) were contaminated above 20 mg kg(-1) and there were no differences between the oat types tested. Only one gluten-free variety of oats was analysed and it consistently provided negative results in all analyses. It is difficult to determine where the contamination originates, but there are possibilities for cross-contamination in the field, in the transport of the grain, in the storage of the grain, and in the milling and packaging facilities. It is clear from this study that only those products that have been certified 'pure' oats would be appropriate for a gluten-free diet.