Reduction of hexavalent chromium was studied in three bench-scale continuous stirred tank reactors. The inoculum was a culture of Pseudomonas sp., capable of giving 83% to 87% chromate reduction in 72-h batch assays with 60 mg Cr(VI) L(-1) in synthetic medium. The continuous culture studies were conducted for about 100 days using synthetic feed containing different levels of chromate (5 to 124 mg L(-1)) at 28 degrees to 30 degrees C and pH 6.8. The feed rate was varied over the range 0.5 to 1 L d(-1) to obtain hydraulic retention time of 36 to 72 h. Chromate reduction efficiency was 81% to 91% and 100% for influent Cr(VI) concentrations of 15 to 124 and 5 mg L(-1), respectively, with a hydraulic retention time of 72 h.