[en] Using the methods of UV and visible spectroscopy, the reduction of pertechnetate-ions in nitric acid and hydrochloric acid solutions has been studied. At [NNO₃]< approximately 8 mol/l the TcO₄^- reduction proceeds to the formation of nitrate complexes of Tcsup((4)) through an intermediate stage of Tcsup((5)). At [HNO₃]>8 mol/l the reduction is realized only to the isolation of Tcsup((5)), in the form of a nitrate complex of the composition T(O(NO₃)₃xH₂O). It is pointed out that two-electron reduction according to the scheme TcO₄^-+N₂H₅⁺ → Tcsup((5)) + N₂ + 2H₂O+ H⁺ is the stage, limiting the summary rate of the TcO₄^- reduction. The mechanism of subsequent reactions is discussed