Aqueous methyldioxorhenium (MDO), prepared from methyltrioxorhenium (MTO) and hypophosphorous acid, abstracts an oxygen atom from tertiary alkyl hydroperoxides. This regenerates MTO and forms the tertiary alcohol with rate constants 3.71 x 10(4) L mol(-1) s(-1) (t-BuOOH) and 3.47 x 10(4) L mol(-1) s(-1) (t-AmOOH) at 25.0 degrees C in aqueous 1.0 M HOTf. MDO reacts with hydrogen peroxide first to form MTO, k = 3.36 x 10(4) L mol(-1) s(-1) which subsequently reacts with more hydrogen peroxide to form peroxorhenium complexes. In a separate study, the concomitant slow decomposition of alkyl hydroperoxides and MTO (to ReO4-) was investigated. The rate law is v = k[MTO][RCMe2OOH]/[H+], with k = 7.4 x 10(-5) s(-1) (R = Me) and k = 8.4 x 10(-5) s(-1) (R = Et) at 25.0 degrees C in aqueous solution at mu 1.0 M. H-1 NMR spectroscopy and GC revealed organic products suggestive of radical reactions. The products from t-BuOOH are acetone, methanol, tert-butyl methyl ether, methane, ethane, and tert-butyl methyl peroxide. With CH2DReO3, it could be shown that both t-BuOOH and MTO were sources of the methane. The rate of decomposition of MTO shows an inverse-first-order dependence on [H+] throughout the range pH 1-6.42.