Technical Abstract: This study evaluated the effects of inhibitors on polyphenol oxidase (PPO) activity, the effect of the PPO inhibitor tropolone on noodle darkening, and the correlation of PPO activity with darkening of alkaline noodles. The PPO inhibitors tropolone and salicylhydroxamic acid (each at 1 'M) reduced kernel PPO activity by approximately 50% in three hexaploid wheat cultivars, but did not inhibit PPO activity in the two very low PPO cultivars, durum 'Langdon', and the synthetic hexaploid-derived 'ID580'. Tropolone (100 ug/g flour) inhibited alkaline noodle darkening ('L*) by 13-25% in the low PPO wheat cultivar, 'ID377s', and by 39-54% in the high PPO wheat cultivar, 'Klasic'. Alkaline noodle darkening among 502 wheat samples was correlated with kernel PPO activity (r = 0.64). Results substantiate the hypothesis that PPO plays a major role in darkening of alkaline noodles. However, results also indicate that substantial darkening would occur even at zero PPO activity, as measured in the kernel PPO assay. Therefore, darkening of alkaline noodles is probably due to the cultivar-specific level of PPO activity and the presence of at least one additional darkening mechanism. Further investigation is required to identify the phenolic discoloration agent(s) and to determine the potential roles of non-PPO discoloration mechanisms, both enzymatic and non-enzymatic, in wheat products.