Analysis of uncertainties in stratospheric perturbations requires the development of a model which uses a minimum of computer time yet is complete enough to represent reasonably the results of more complex models. Such a concise model has been developed and is described in this paper. The model is a steady state model using iteration to achieve coupling between interacting species. The species odd oxygen, H2O, H2, CO, N2O, odd nitrogen, CH4, CH3Cl, CCl4, CF2Cl2, CFCl3, and odd chlorine are determined from diffusion equations with appropriate sources and sinks. The HOx species, methane oxidation products, and relative species abundances within the odd oxygen, odd nitrogen, and odd chlorine families are solved in photochemical equilibrium, and N2, O2, CO2, and temperature have been assigned fixed profiles. Diurnal effects such as those due to chlorine nitrate formation are accounted for by analytic approximations. The model has been used to evaluate steady state perturbations due to injections of chlorine and NOx. The results are similar to those obtained by other models.