The isomerizations and decompositions of cis- and trans-2,3-dimethyloxirane were studied behind reflected shocks in a pressurized driver single-pulse shock tube over the temperature range 900:1150 K and overall densities of similar to 3 x 10(-5) mol/cm(3). In addition to a cis reversible arrow trans structural isomerization, four isomerization products, methyl ethyl ketone, isobutyraldehyde, ethyl vinyl ether, and 2-butene-3-ol, were obtained under shock heating. A large number of decomposition products were also obtained. The major ones in decreasing order of abundance were CO, C2H4, C2H6, and CH4. In a similar manner to the decomposition of oxirane and methyloxirane, the free-radical reactions in the present system are initiated by a direct decomposition of a thermally excited methyl ethyl ketone which is produced in the course of the isomerization. A reaction scheme composed of 41 species and 65 elementary reactions accounts for the product distribution over the entire temperature range of this investigation provided decomposition channels of thermally excited isomers are included in the scheme. The rate constants obtained for the isomerization reactions are in good agreement with the values extrapolated from low temperatures. First-order Arrhenius rate parameters for the formation of the various reaction products are given and a sensitivity analysis for their production is summarized.