The problem of simultaneous convection, diffusion and reaction inside a porous catalyst slab is considered. A combination of perturbation and integral mathematical techniques are used to derive approximate analytical solutions for the concentration and temperature profiles, as well as for the maximum temperature and the effectiveness factor, for a first order, nonisothermal reaction. Three regimes of operation are characterized: regime I, in which convection and diffusion are dominant (small Thiele modulus); regime H, in which diffusion and reaction are dominant (large Thiele modulus); and regime III, in which convection and reaction dominate (intermediate Thiele modulus). Our analytical solutions for each of these regimes are validated by comparison with previous results from numerical simulations. (c) 2007 American Institute of Chemical Engineers.