Technical Abstract: The potato can make a significant contribution of antioxidants to the human diet. In this study, antioxidant levels in tubers of 16 clones grown at four production sites (two conventional, two organic), both fresh and stored, were examined across two years. Antioxidant activity of fresh tubers at all locations was higher in 2006 than in 2005. Cooler late-season temperatures in 2006 may have been responsible for the increased levels of antioxidants. Stored tubers had higher levels of antioxidant activity than fresh tubers, with a larger storage effect in 2005, when antioxidant levels in fresh tubers were lower. There was no consistent effect of production system (organic versus conventional) on antioxidant activity in tubers. For the clones we evaluated, antioxidant levels were generally highest in potatoes grown in high-yielding production environments.