High energy neutrino-electron and neutrino-nucleon collisions are discussed. In particular the “elastic” processes ν + p → n + e+ and ν+ n →p + e- are investigated in detail. The cross section of ν+ n →p + e- is estimated to be ∼0.8 ×10-38 cm2 for neutrino energy in lab system > 1 Bev under the reasonable assumptions.