Accurate quantitation of any contaminant of interest is critical for exposure assessment and metabolism studies that support risk assessment. A preliminary step in an arsenic exposure assessment study in Nevada quantified total arsenic (TAs) concentrations in tissues as biomarkers of exposure. Participants in this study (n=95) were at least 45 years old, had lived in the area for more than 20 years, and were exposed to a wide range of arsenic concentrations in drinking water (3-2,100 ppb). Concentrations of TAs in blood, urine, and toenails determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) ranged from below detection to 0.03, 0.76, and 12 ppm, respectively; TAs in blood rarely exceeded the limit of detection. For comparison, TAs in toenails determined by neutron activation analysis (NAA) ranged from below detection to 16 ppm. Significant (P<0.0001) positive regressions were seen between the TAs concentration in toenails and in drinking water (adjusted r(2)=0.3557 HG-AFS, adjusted r(2)=0.3922 NAA); TAs concentrations in urine were not described by drinking water As (adjusted r(2)=0.0170, P=0.1369). Analyses of TAs in toenails by HGAFS and NAA yielded highly concordant estimates (r=0.7977, P<0.0001). These results suggest that toenails are a better biomarker of chronic As exposure than urine in the current study, because the sequestration of As in toenails provides an integration of exposure over time that does not occur in urine.