[en] A simple radiochemical neutron-activation method for the determination of arsenic in rock is described. After fusion with mixture of sodium peroxide and separation of the insoluble hydroxides, arsenic is determined in the filtrate fraction, by a single precipitation of the sulphides after acidifying with hydrochloric acid and dissolved in aqua regia. Chemical yields (about 90%) is determined by reactivation of the dissolved sulphide. The accuracy and precision of the method is high, as demonstrated by the analysis of standard reference materials (Soil-5, S L-1 and 1633 a). The method can be applied to geochemical studies of arsenic in rocks and minerals