Palladised biomass of Desulfovibrio desulfuricans ATCC 29577 (bio-Pd(0)) effected reduction of Cr(VI) to Cr(III) under conditions where biomass alone or chemically-prepared Pd(0) were ineffective. Reduction of 500 mumol dm(-3) Cr(VI) by 0.4 mg cm(-3) bio-Pd(0) (Pd:biomass ratio of 1: 1) was achieved from 1 mol dm(-3) formate/acetate buffer at pH 1-7 at room temperature; the optimum pH was 3.0. The ratio of mass of Pd: dry mass of biomass, and the need for finely ground bio-Pd(0) were important parameters for optimal Cr(VI) reduction, with a ratio of 1:1 giving 100% reduction of 500 mumol dm(-3) Cr(VI) within 6 h at room temperature, decreasing to 30 min following heat treatment of the Pd(0)-loaded biomass. The reduced Cr was recovered quantitatively as soluble Cr(III) at pH 3.0 with no poisoning of the bioinorganic catalyst with respect to continued reduction of Cr(VI).