Experimental concentration measurements of the major stable species and five radical species (OH., H atom, O atom, CH., and CH3) obtained on a rectangular Wolfhard-Parker slot burner are compared with a detailed computation of the chemical structure of an axisymmctric laminar, CH4/air diffusion flame burning at atmospheric pressure. In order to examine these CH4/air flames with different geometries and different sizes, the species profiles are plotted as functions of the local mixture fraction, and the scalar dissipation rate has been matched in a region around the stoichiometric surface. The overall agreement in the absolute concentrations, the shape of the profiles, and their location in terms of the local mixture fraction is good to excellent for the stable species (except for O2) and for the most abundant radicals OH, H atom, and O atom. For example, the calculated OH- maximum concentration is in much better agreement with the experimental results than are full equilibrium and partial equilibrium estimates. Less satisfactory agreement is found for the CH. and CH3radicals. In addition, significant discrepancies are observed in the temperature field and in the degree of O2penetration into rich flame regions.