Abstract Arsenic determination was carried out on hair, urine, and blood samples taken from groups of 10-year old boys, each numbering 20 to 25 individuals, residing in a region polluted by arsenic. The source of arsenic emissions ( 1 2 to 1 ton per day) is a power plant burning local coal of high arsenic content. In all the materials examined, considerably elevated concentrations of arsenic were found. The relation of the observed levels of arsenic to the distance of the place of residence up to a distance of more than 30 km from the source of the emissions was studied. On the basis of the results obtained, the most advantageous material for estimation of nonoccupational exposure to this toxic agent seems to be hair, in spite of some problems with the decontamination procedure involved. The results corresponded to the theoretical ideas on spreading of emissions from elevated sources in the open air and tend to establish the applicability of arsenic determination in the hair as a direct exposure test of contamination of the environment by arsenic. Considerable variablility among individual arsenic values in the hair makes group examination a necessity. The same applies to the urine and blood sampling, which is complicated by several technical difficulties. Levels in urine reflect the quantities of arsenic inhaled or ingested after their absorption into the blood, and give a more realistic picture of possible daily intake.