We examined the variability of blueberry fruit antioxidant activity (AA) among nine genotypes harvested in Minnesota (MN), Michigan (MI), and Oregon (OR) in 1998 and 1999 to determine the effects of genotype and environment on AA, total anthocyanin content (ACY) and total phenolic content (TPH). Genotypes differed significantly (P<0.05) in AA, ACY, and TPH both within and among locations. There were significant changes in genotype rank for AA, TPH, and ACY among all locations and between years within each location. 'Bluegold' and 'Northland' had the highest overall AA. Pearsonís correlation for AA (based on genotype means) appeared highest between MN and OR (0.90) and MN and MI (0.69) in 1998, with correlations between locations for the combined years being 0.74 for MN and OR, 0.55 for MN and MI and 0.45 for MI and OR. For the group of nine cultivars, AA correlated well with TPH within each location: 0.88 in MN, 0.75 in OR, and 0.89 in MI for combined years. Correlation of AA with ACY at each location was lower than that for AA with TPH, in both individual and combined years. This study demonstrates significant genotype x environment interaction for AA in blueberry.