Boson instability of charged black holes

The processes of spontaneous and induced creation and accumulation of charged bosons on quasi-bound superradiant levels in the field of a Kerr-Newman black hole is analysed. It is shown that bosonic instability may be caused exclusively by the rotation of the black hole. Particularly, the Reissner-Nordström configuration is stable. In the case of a rotating and charged black hole the bosonic instability may cause an increase of charge of the black hole.