The color of wheat end-products depends on flour characteristics, including polyphenol oxidase (PPO) level, in addition to processing. The purpose of this study was to evaluate the methodologies used to determine PPO activity, to compare the effects of genotype and environment on PPO, and to determine the relationship of PPO to end-product discoloration. A set of double haploid experimental lines, including red and white kernel genotypes and agronomical checks, were grown at four locations in western Canada during two years. PPO activity was analyzed in grain and flour by the oxygen consumption method with catechol as substrate, and by spectrophotometric methods. Color values and discoloration after 24 hours were determined in salted (Udon) and alkaline (Kansui) type noodle sheets. A simple fast spectrophotometric whole kernel method using tyrosine as a substrate was well correlated with results of the oxygen consumption method (r = 0.813, P = 0.001). Milling and flour properties of the samples were affected significantly by the environment. (Abstract shortened by UMI.)