Flavor changing models with strictly massless neutrinos

Theoretical models which present flavor changing neutrino interactions and simultaneously prevent this particle from acquiring any mass exist. We discuss some of them and their predictions for neutrino oscillations in matter which can account for the solar neutrino anomaly as well as the zenith-angle dependence of the deficit of atmospheric neutrinos observed by the SuperKamiokande experiment without invoking, therefore, neutrino masses nor mixing.