The concentration of chromium in environmental and biological samples (ground, sea, and drinking water, blood serum, urine) is too low (0.1-1 ng/ml) to be determined directly from the sample with either flame atomic absorption, ICP/AES, or even ICP/MS methods. To determine the Cr(III) and Cr(VI) content of these samples is even more difficult. To solve this problem we combined a high-pressure liquid chromatographic separation method with atomic spectrometric detection. In addition to the Cr(VI) preconcentration, a new on-line preconcentration/elution method with a C18 HPLC column was developed to determine the Cr(III) concentration. For the preconcentration, in the case of Cr(VI), 0.05 M tetrabutylammonium bromide was used as an ion pair forming agent while 0.075 M potassium hydrogen phthalate was used to preconcentrate Cr(III). The eluent was a methanol-water mixture of 60% or 80%, respectively. One of the most effective methods of atomic spectrometry, hydraulic high-pressure nebulization, was used for sample introduction. In a comprehensive study, flame emission spectrometry with a stoichiometric nitrous oxide/acetylene flame proved to be the most effective detector to analyze Cr(III) and Cr(VI). Samples of 5 ml were preconcentrated and eluted with 1 ml of methanol; the l Å 425.43 nm emission line of chromium was used for detection. Under these conditions the detection limit (3s) was 25 pg/ml for Cr(III) and 20 pg/ml for Cr(VI). The relative standard deviations (N Å 10) are 5.6 and 2.1% for 1 mg/l Cr(III) and Cr(VI), respectively. These achievements allowed the determination of the toxic Cr(VI) content of surface and drinking water samples.