<p>The quasi-steady-state approximation of chemical kinetics consists of equating to zero the time derivatives of the concentrations of intermediate species in the rate equations. It is remarkably successful in simplifying those equations, but that does not imply that any conclusions drawn are correct. Singular-perturbation theory has proved effective in deciding such questions, but is not easily accessible to non-mathematicians. It is therefore valuable to explore whether other methods can usefully contribute to our understanding of the (sometimes nonlinear) differential equations arising in chemical kinetics.</p>