The rate of oxygen uptake in the initiated oxidation of isopropanol inhibited with salts of Cu(II), Fe(HI), Co(II), and Mn(II) was studied depending on the concentration of sulfuric and perchloric acids. It has been found that the acid in the concentration of ca. 2 x 10(-3) mol/l completely stops the inhibition with the cobalt and manganese salts. The efficiency of inhibition by copper and iron salts is not affected by adding the acids. The action of acids is inconsistent with the conventional concepts of the earlier proposed mechanism of negative catalysis common for various metals.