['To explore the influence of folate-fortified foods (ready-to-eat [RTE] breakfast cereals or fruit-juice drinks) on the relation between the methylenetetrahydrofolate reductase (MTHFR 677C>T) polymorphism and plasma total homocysteine (tHcy) concentrations in healthy children.', 'This was a cross-sectional study by face-to-face interview. A total of 186 sixth-grade students participated from randomly selected primary schools in Volos, Greece. Fasting plasma tHcy, folate, and vitamin B12 were measured. The MTHFR genotypes were determined. Anthropometric data were collected and dietary intake was assessed by two non-consecutive 24-h recalls. Participants were characterized as non-consumers of RTE breakfast cereals or fruit-juice drinks if there was no report of any such food during the 24-h recall interviews; all other children were classified as consumers.', 'Geometric means for plasma tHcy were higher, whereas plasma folate was lower in non-consumers compared with consumers. The sample was divided by consumption status (yes or no) to explore the significance of each polymorphism depending on consumption status. The association between the genotype and tHcy was restricted to non-consumers (P<0.05). Specifically, only in children who did not consume RTE breakfast cereals or fruit-juice drinks did the TT genotype carriers exhibit higher tHcy concentrations when compared with C-allele carriers (P<0.05). In contrast, in consumers, circulating tHcy was similar regardless of genotype.'] Is effect of the methylenetetrahydrofolate reductase ( MTHFR 677C > T ) polymorphism on plasma homocysteine concentrations in healthy children influenced by consumption of folate-fortified foods?