Abstract The reaction of TsiSiMe 2H (I) (Tsi = (Me 3Si) 3C) with I 2 or with a molar equivalent of ICl gives the iodide TsiSiMe 2I (II) in hydroxylic media (MeOH, CH 3CO 2H, CF 3CO 2H) as it does in CCl 4. The reaction with I 2 is very fast in CF 3CO 2H, but in MeOH is only about as fast as in CCl 4. The iodide II reacts with ICl in MeOH to give a mixture of TsiSiMe 2OMe (III) and TsiSiMe 2Cl (IV), but the reaction is markedly slower than that in CCl 4 (in which IV is formed). The hydride I also reacts with INO 3 in MeOH to give II, and the latter reacts with INO 3 to give III. The reactions of TsiSiPh 2H (V) and TsiSiPh 2I (VI) with ICl in MeOH are markedly slower than those of I and II; even with one equivalent of ICl in MeOH, V gives a mixture of VI and the (rearranged) methoxide (Me 3Si) 2C(SiPh 2Me)(SiMe 2OMe) (VII). Reaction of VI with ICl in MeOH gives VII and the rearranged chloride (Me 3Si) 2C(SiPh 2Me)(SiMe 2Cl). The formation of methoxides in the reactions of the iodides II and VI with ICl in MeOH, and the rearrangements observed in the case of VI, are consistent with a mechanism involving an intermediate silicocation. Other mechanistic aspects are discussed.