Radiative decays of massive neutrinos

General formulas are given for the decay rate ${\nu }_2\to {\nu }_1+\gamma$ in the SU(2)×U(1) model for neutrinos with a small mass. The emphasis is on distinguishing between the cases of Dirac and Majorana neutrinos. Possible enhancements of the rate due to methods of eluding the Glashow-Iliopoulos-Maiani suppression and due to charged Higgs bosons are considered.