In this paper, ToF-SIMS was used to study the Pd-Rh interdiffusion which has a great interest in brachytherapy, a cancer treatment. The secondary ion mass spectrometry was used in the semi-quantitative MCs+ mode, by detecting the RhCs+ and the PdCs+ molecular ions under cesium bombardment. At first, different RhxPdy (from pure Rh to pure Pd) layers were deposited by PVD and were subsequently characterized by ToF-SIMS, RIBS and PIXE. A linear relationship between the relative CsPd+ yields and the Pd concentration into the Rh matrices was found. Moreover, the total sputtering yield increases linearly with the Pd concentration. Those relationships permitted to calibrate the ToF-SIMS depth profiles of annealed Pd/Rh layers and were successfully used to quantify the Pd-Rh interdiffusion. (c) 2006 Elsevier B.V. All rights reserved.