The analysis of urine, blood, and hair has been used previously to monitor occupational exposure to arsenic (As). Although arsenic is normally present in human fingernails (usually as a result of dietary factors), this study evaluated the potential use of levels of arsenic in fingernails as a biological indicator of occupational exposure to this element. Air samples and fingernail clippings were obtained from individuals with no exposure and high, medium, and low exposure. A washing technique, previously developed to remove exogenous arsenic from hair, was modified to wash the fingernail samples collected in this study. It was demonstrated that 98% of exogenous arsenic was removed from these nails. A high correlation coefficient (r = 0.89) was observed in a comparison of the mean air arsenic concentrations of each exposure group with corresponding arsenic levels in fingernails. From the data collected, an equation was derived to estimate the air arsenic exposure level for a worker from the arsenic content of fingernails: air arsenic concentration (micrograms As/m3) = 1.79 x fingernail arsenic level (micrograms As/g nail)-5.9.