Proof of concept was obtained that nitrobenzene can be reduced to aniline by a mixed reductive microbial culture using H-2 as the sole electron donor source. In a continuous-flow anaerobic bioreactor, both pH and temperature affected nitrobenzene reduction with optima of pH 6.5-6.8 and 30degreesC. The efficiency of nitrobenzene degradation increased with H-2 up to 10% (v/v). An increase in sulfate concentration decreased the removal rate of nitrobenzene.