Solvent effects on the disrotatory ring opening of cyclopropanone and 2,2-dimethylcyclopropanone have been computed by Monte Carlo simulations at 25 degrees C, Geometries for the cyclopropanones, the transition state for the rearrangement of cyclopropanone, and the oxyallyls were obtained from ab initio (4/4) CASSCF calculations with the 6-31G* basis set. For each geometry, CHELPG and Mulliken charges were determined for use in the fluid simulations. Statistical perturbation theory yielded the changes in free energies of solvation in four solvents for the ring openings. The modest computed solvent effects are in good accord with experimental data of Greene and coworkers. Our results support the intermediacy of oxyallyls in cyclopropanone stereomutations, indicate the proximity of the oxyallyls to the transition states for the ring openings, and confirm the principally diradical rather than zwitterionic nature of the oxyallyls.