Folate degradation in micronutrient fortified corn masa and tortillas was evaluated using masa prepared from either nixtamalized corn flour or fresh nixtamal. A laboratory evaluation of the effects of pH, iron, and holding time at elevated temperature on folate loss in corn flour masa failed to show significant differences in any variable-treatment combination. An additional study was conducted at a commercial tortilla mill in Guadalajara, Mexico using masa prepared from fresh nixtamal. Commercial nixtamal was fortified with one of two different micronutrient premixes, containing iron, zinc, riboflavin, thiamin, niacin and either unencapsulated or lipid-encapsulated folic acid. A batch of each fortified masa and an unfortified control batch were prepared on each of two consecutive days. Folate loss in prepared masa increased with prebake masa holding time for both premixes. Encapsulated folic acid showed a significantly lower percent loss from theoretical, indicating a protective effect from the lipid coating. No significant differences in folate levels were found between prebake masa and baked tortillas. Holding baked tortillas for up to 12 hours also had no effect on folate levels. Results indicate that added folic acid is degraded during the grinding process, as well as during pre-bake holding of masa. Native folate showed no significant loss.