The decomposition of nitromethane was studied over the temperature range 1000-1100 K in reflected shock waves. CH3NO2 and the reaction products were analyzed by gas chromatography. The derived gross rate constant and activation energy for the disappearance of CH3NO2 is consistent with that of Glanzer and Tree. A reaction mechanism consisting of 99 chemical reactions was developed to simulate the experimental data of the present study and that of Hsu and Lin. Good agreement between experiments and simulations was achieved. It appears that significant amounts of CH3NO2 are destroyed through secondary reactions that involved highly reactive free radicals (H, OH, and CH3), suggesting the need for redeterming the mle unimolecular decay rate constant for CH3NO2. For improvement of the performance of the model, several other rate constants also need to be determined. The final section is a preliminary report on a spectrophotometric technique for measuring the loss of nitromethane due to pyrolysis by recording its absorption of UV radiation, directed axially along a small diameter shock tube. Although only semiquantitative data were obtained, this novel procedure merits discussion.