The associations between As levels in fingernails with both As concentrations in urine and environmental samples are reported. The participants (aged 20-80 years, mean 66 years) lived in the vicinity of a coal-burning power plant with high As emissions in the Prievidza District, Slovakia. Samples were taken in 1999 and 2000. The As levels in fingernails (n ¼ 524) were measured after washing and digestion with microwave heating by hydride generation atomic absorption spectrometry. The spot urine samples (n ¼ 436) were speciated for inorganic As (As inorg ), monomethylarsonic (MMA) and dimethylarsinic acid (DMA) by hydride-cryogenic trap-atomic absorption spectrometry. The geometric mean As level in fingernails was 0.10 mg/g (range, o0.01-2.94 mg/g). There was a clear association between As in fingernails and the distance of the home to the power plant (Po0.001). Geometric mean As levels were: 0.17 mg/g distance r5 km, 0.10 mg/g 6-10 km and 0.08 mg/g 4 10 km. The association between the distance to the power plant and total urinary As (As sum ) (n ¼ 436, no fish consumption during the last 3 days before sample collection) was less pronounced (P ¼ 0.018). The As levels in fingernails were positively correlated to As in soil (n ¼ 207, r ¼ 0.23, Po0.001) and to As in house dust (n ¼ 209, r ¼ 0.30, Po0.001). The associations between urinary As sum and As concentrations in soil (n ¼ 159, r ¼ 0.13, Po0.105) and in house dust (n ¼ 162, r ¼ 0.14, Po0.081) were quite similar. As levels in fingernails were associated with urinary As sum and with the different As species in urine. It is concluded that As levels in fingernails are a reliable marker of environmental As exposure, and that As concentrations in fingernails reflect the As exposure in a similar manner compared with urinary As sum and As species.