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NAD(P)H:quinone oxidoreductase (NQO1) is an inducible detoxification enzyme relevant for colorectal cancer biochemoprevention. We evaluated the influence of recent fruit and vegetable (F&V) consumption and polymorphisms in NQO1 and transcription factor NFE2L2 on rectal NQO1 phenotype and also whether white blood cell (WBC) NQO1 activity reflects rectal activity. Among 94 sigmoidoscopy patients, we assessed F&V consumption by dietary record and determined the NQO1 c.609C > T and g.-718A > G and NFE2L2 g.-650C > A, g.-684G > A, and g.-686A > G polymorphisms. NQO1 mRNA level was measured in rectal biopsies and NQO1 activity in rectal biopsies and WBC. Consumption of F&V did not yield higher mRNA level or activity but rather appeared to have a repressive effect. Rectal activity was higher among NQO1 609CC-genotypes as compared to 609CT-genotypes (P < 0.0001; 609TT-genotypes were absent), whereas mRNA was higher among 609CT-genotypes (P < 0.001). mRNA and activity correlated among NQO1 609CC-genotypes (r = .50, P = 0.0001) but not among 609CT-genotypes (r = .14, P = 0.45). The NFE2L2-684A-allele was associated with higher mRNA levels (P = < 0.05). The other polymorphisms did not affect phenotype significantly. WBC and rectal activity did not correlate. In conclusion, genetic variation, especially the NQO1 609C > T polymorphism, is a more important predictor of rectal NQO1 phenotype than F&V consumption. WBC NQO1 activity is not a good surrogate for rectal activity.