In recent years there has been growing interest in the vitamins folic acid and vitamin B12 because of the realization that the status of these vitamins in populations is less than adequate, and that such inadequacy may be linked to adverse public health outcomes. This concern has prompted the United States, Canada, and other countries to fortify grain products with folic acid, while additional countries are considering doing so in the near future. This presentation provides a new approach which relies on the combination of the concentrations in blood of vitamins and their respective functional indicators to establish cutoff points for assessing folate and vitamin B12 status in populations. The premise is based on the fact that the relationship between plasma vitamin concentrations and their respective functional indicators is inverse and biphasic, with a steep slope at low concentrations of the vitamin and a more moderate slope at higher plasma vitamin concentrations. We propose that the intersection of these two slopes be used as a guideline for assessing the status of these vitamins and the adequacy of fortification programs. The cutoff would be 10 nmol/L for serum folate and 340 nmol/L for red blood cell folate, based on lowest plasma homocysteine. For serum vitamin B12, the cutoff would be 150 pmol/L based on lowest methylmalonic acid and 300 pmol/L based on lowest homocysteine.