A new coprecipitation procedure is presented for the speciation of Cr(III) and Cr(VI) on neodymium(III) hydroxide precipitate. Chromium determination was performed by flame atomic absorption spectrometry. Total chromium was determined by application of the same procedure after reducing Cr(VI) to Cr(III). The concentration of Cr(VI) was calculated by the concentration difference between total Cr and Cr(III). The optimal parameters that affected the quantitative recoveries of Cr(III) were investigated. The influences of co-existing ions were controlled. The detection limit and preconcentration factor for Cr(III) were 2.1 mu g/L and 100, respectively. The method was applied to the speciation and determination of chromium in natural water samples.