In a rural Negro population subsisting on a predominantly maize meal diet, the incidence of folate deficiency was 43.8% in nonanaemic women in late pregnancy, 32.1% in nonpregnant women, and 18.6% in adult males. More than one-third of all subjects older than 60 were deficient. No instance of unequivocal vitamin B12 deficiency was revealed in 431 subjects sampled, and it is considered that the hazards of giving a small daily dose of folic acid in this population are negligible. These findings warrant food fortification with folic acid in this and similar population groups.