It has been shown that iron(III), copper(II), and manganese(II), common contaminants of alkali-metal hydroxides, not only enhance the rate of alkali-induced decomposition of hydrogen peroxide, but also result in the rate maximum being observed at a different pH value of 11.6, 12.0, and 9.5, respectively. Different methods are recommended for the production of high-purity alkali solution and removal of contaminants. The addition of ethylenediaminetetra-acetic acid (H₄edta) to the reaction mixture resulted in a further decrease in the decomposition rate and three stages could be distinguished in the rate vs. time curves. The lowest rate (stage II) is proportional to the square of the hydrogen peroxide concentration and to the hydroxide-ion concentration. During this stage, formation of hydroxyl and superoxide radicals was observed. It is believed that the true rate of the alkali-induced decomposition of hydrogen peroxide can be determined if purified alkali and chelating agent are simultaneously employed: the rate coefficient is 3 × 10^–6 dm³ mol^–1 s^–1 at pH 11.6, 10^–3 mol dm^–3 H₄edta, and 0.1 mol dm^–3 H₂O₂ at 308 K.