The near-surface erosion rate in SIMS depth profiling is significantly different from that in the bulk, and varies with primary ion dose across the transient region in a currently unknown manner. Here, we describe a new method using medium energy ion scattering to measure the transient matrix sputter yield, and hence determine the erosion rate. We demonstrate its use in converting the raw dose and yield scales in a shallow depth profile to depth and concentration. We show that the surface erosion rate may be more than 10 times that in the bulk, and that the ion yield for boron in silicon apparently stabilizes before the sputter yield. (C) 2002 Elsevier Science B.V. All rights reserved.