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 = 524) were measured after washing and digestion with microwave heating by hydride generation atomic absorption spectrometry. The spot urine samples (n = 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 mug/g (range, <0.01-2.94 microg/g). There was a clear association between As in fingernails and the distance of the home to the power plant (P<0.001). Geometric mean As levels were: 0.17 microg/g distance < or = 5 km, 0.10 microg/g 6-10 km and 0.08 microg/g > 10 km. The association between the distance to the power plant and total urinary As (As(sum)) (n = 436, no fish consumption during the last 3 days before sample collection) was less pronounced (P = 0.018). The As levels in fingernails were positively correlated to As in soil (n = 207, r = 0.23, P<0.001) and to As in house dust (n = 209, r = 0.30, P<0.001). The associations between urinary As(sum) and As concentrations in soil (n = 159, r = 0.13, P<0.105) and in house dust (n = 162, r = 0.14, P<0.081) 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.