The reduction of chromate (2 10 - 4 mol dm - 3 ) by l-ascorbate (0.95-5.71) 10 - 3 mol dm - 3 ) has been studied by spectrophotometry under aerobic and anaerobic conditions. Phosphate, HEPES and Tris-HCl buffers were used in pH range 6.8-7.8 with T = 25/26°C, I = 0.5/1.0 mol dm - 3 , [O 2 ] = 0.03-7.17 mg l - 1 . The reaction was confirmed as first order with respect to both reactants. The rate determining step is suggested as formation of a chromate-ascorbate-ester. In phosphate and HEPES buffers the experimental, pseudo-first-order rate constants obtained in the absence of dioxygen were almost identical to those obtained in its presence. However in the presence of Tris-HCl buffer an oxygen dependence of the reaction was observed. This suggests that inhibition of the rate constant by dioxygen is a buffer dependent effect and is not an intrinsic feature of the redox reaction between chromate and ascorbate. The implications of these results for the mechanism of chromate toxicity are discussed.