Many industrial wastes contain Cr(VI), a carcinogen and mutagen, the toxicity of which can be ameliorated by reduction to Cr(III). Microbacterium sp. NCIMB 13776 and Desulfovibrio vulgaris NCIMB 8303 reduced Cr(VI) to Cr(III) anoxically using 25 mM sodium citrate buffer (pH 7), with 25 mM sodium acetate and 25 mM sodium formate as electron donors at 30 degreesC, under which conditions the rates of reduction of 500 muM sodium chromate were 77 and 6 nmol h(-1) mg dry cell wt for D. vulgaris and Microbacterium sp., respectively, these being increased to 127 and 17 nmol h(-1) mg dry cell wt in the presence of 20 mM MOPS/NaOH buffer.