A numerical mass transfer analysis for plane and square duct geometries for developing and fully-developed scalar transport with laminar flow is described. A methodology for prescribing stream-wise periodic scalar boundary conditions under conditions of constant-transformed-substance state, is detailed. The solution to the fully-developed mass transfer problem is presented in terms of driving force, blowing parameter and normalised conductance. A suitably-defined polarisation factor is shown to be functionally equivalent to the former. The data compress onto a single curve with good correspondence to the 1-D convection-diffusion solution, except for high rates of wall injection or suction. (c) 2005 National Research Council of Canada. Published by Elsevier Ltd. All rights reserved.