A method for Cr determination in biological samples based on proton nuclear activation is presented. The activation was induced by a 13.8 MeV proton beam of the AVF Cyclotron of Milan University via a (p, n) reaction on the nuclei of the target. For the quantitative determination Cd has been chosen as reference element. The method has been applied to Cr determination in human serum samples. The experimental procedure is described and results are presented and discussed.