Maize grains were treated with electromagnetic fields and nixtamalized with nejayote, in order to analyze the effect of such treatments on the microbiological and viscoelastic properties of masa, and on sensory tests of tortilla. A sample of maize grains was irradiated by electromagnetic fields for 7 and 12 min. Then, following the nixtamalization with nejayote, masa and tortillas were obtained. The application of electromagnetic fields did not decrease the growth of moulds in maize grains. However, a synergistic effect of irradiation (12 min) and nixtamalization with diluted nejayote (50 water/50 whole nejayote) improved the sanitary quality of masa. Elastic and viscous moduli showed significant differences in all treatments. The masa from maize grains irradiated for 12 min showed the highest values of elastic and viscous moduli, while the masa from grains irradiated for 7 min and nixtamalized with diluted nejayote (70 water/30 whole nejayote) presented the lowest values. These results seem to indicate that the application of electromagnetic fields modifies the viscoelastic modulus of masa. Sensory tests showed that tortillas obtained from irradiated (12 min) maize grains, nixtamalized with nejayote (70 water/30 whole nejayote), had the highest score of all the attributes, i.e. texture, chewiness and taste.