An important aspect of studies on the fate of organic pollutants is identification of environmental agents that are responsible for observed degradation reactions. To this end, many studies using natural water, soil, or sediment as a medium rely heavily on autoclaved control experiments to distinguish abiotic from biotic processes. The effect of autoclaving on the acid/base and redox properties of anaerobic sediment slurries was determined to facilitate the interpretation of autoclaved controls in studies of environmental reduction reactions. Autoclaving decreased electrode measurements of pH by 0.26 to 0.68 units and increased electrode measurements of Eh by 34 to 94 mV. To corroborate this effect, the authors added redox indicators to the slurries and observed that autoclaving caused a shift in color consistent with the change in electrode measurements. Further investigation demonstrated that the observed effects are a common characteristic of autoclaving anaerobic sediment and are not limited to very restricted sediment types and are not artifacts of the way the experiments were performed.