Hydrogen gas is assumed to be injected through the surface of a ‘fuel spher’ into a pure oxygen atmosphere, and so to give rise to a spherical diffusion flame. The combustion process is presumed to be sustained by a set of five reactions which involve the six species H2, O2, O, H, OH and H2O, and a proper multi-component, variable diffusion-coefficient, description of the diffusion processes is therefore adopted. Use of the method of matched asymptotic expansions to solve the governing conservation equations makes it possible to deal analytically with this problem and, by focussing attention on the dominance of certain physical phenomena in special regions of the field, reveals the influence of chemical kinetics on flame structure. For example, inner region (i.e. intense reaction zone) behaviour indicates the crucial role played on the O2-rich side of the flame by the reaction OH + H; in one case it may produce O + H2and in the other (with the aid of a third body) it may result in H2O and so act as a chain-breaking step. The relative rate of progress of these two reactions is shown to have an essential effect on the flame structure.