Error functions, which offer solutions to a wide variety of diffusion problems, contain unknown physical parameters in a nonlinear way. We propose a simple iterative method that takes advantage of the geometry of these functions. The method rests on simple analytic relations between the parameters and the first two moments of the distribution. The requisite numerical integrations do not add noise to the data as do methods that estimate slopes. Our method is applied to measured profiles in LPE (GaAl) As. It is simple, efficient and accurate. © 1981, The Electrochemical Society, Inc. All rights reserved.