The rate constants for the reactions of nitrobenzene with the hydroxyl radical (OH.) and hydrated electron in water have been measured from room temperature to 400 degreesC using electron pulse radiolysis and transient absorption spectroscopy. The diffusion-limited reaction of nitrobenzene with (e(-))(aq) exhibits temperature-insensitive activation energy up to 300 degreesC, indicating that the activation energy for electron diffusion remains high over this range. The (e(-))(aq) reactivity is explained as a long-range electron transfer, and the results are interpreted in terms of extended Marcus theory and Smoluchowski relationships. At 380 degreesC, the rate constant has a density dependence similar to that previously reported for other (e(-))(aq) scavenging reactions. The reaction rate of nitrobenzene with OH. is very insensitive to temperature from room temperature up to 300 degreesC, in agreement with previous studies. Above 300 degreesC, the rate constant increases as the critical temperature is approached and exceeded. Time-resolved electronic absorption spectra of the nitrobenzene radiolysis transients reveal complex kinetics involving multiple absorbing species.