Shock waves of 1 mu s duration and peak temperatures from 900 to 1400 K and pressures from 6 to 16 GPa have been applied to measurement of the rates of a broad spectrum of organic compounds including decomposition of explosives. All reaction rates are consistent with known activation parameters and reaction conditions, and there is no indication of unique chemical processes connected with the subnanosecond rise time of the shock front. Reactions having both positive and negative activation volumes have been studied. Extreme pressure favors ionic reaction mechanisms, whereas extreme temperature favors homolytic mechanisms. Either influence may dominate; thus, cyclohexyl nitrate in benzene gives cyclohexylbenzene by a reaction of Friedel-Crafts type, whereas neopentyl nitrate undergoes homolysis, beta-scission, and recombination to give 2-nitro-2-methylpropane. When methanol is used as a solvent, it ionizes extensively and promotes a variety of reactions which ordinarily require acid or base catalysis such as ester interchange and addition of methanol to olefinic bonds.