We consider the problem of mass transfer in a channel with wall reaction and present approximate results to describe the conversion profile. We report analytical solutions in both Graetz's and Leveque's regime in cases where only (semi)numerical studies have been presented before. In particular, for first-order kinetics under conditions of a fully developed concentration profile, an approximate procedure for conversion calculation is proposed for finite reaction rates. When the profile is developing, asymptotic limits are used to formulate accurate approximations in intermediate parametric ranges. Moreover, the effect of finite reaction rates in the corrections due to curvature or velocity profile nonlinearities are reported. Finally, we extend the previous results to an mth order "power-law" wall reaction, so that kinetic normalization is achieved in suitable limits. These results are of relevance for the modeling and simulation of processes involving catalytic monoliths or microreactors. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 2870-2887, 2011