The nano-SIMS 50 allows ion imaging to be performed on microtomed hair cross-sections in order to determine the concentration and to localize the distribution of arsenic traces in hairs. Our study shows a linear relationship between the SIMS signal (As normalized with respect to CN) and the concentration determined by other analytical techniques. The advantages of SIMS imaging can be clearly proved by the capability to record quantitative distributions of As in the cross section. As a matter of fact, the nano-SIMS 50 images may allow differentiation between As located in the medulla, the cortex and the cuticle of the hair and thus distinguish between intoxication by indigestion and surface pollution of the sample. (C) 2004 Elsevier B.V. All rights reserved.