Emission reductions could be provided by cleaner technologies as well as substitution towards less polluting inputs and goods. We develop a model to assess the scope for emission reductions by input substitution. We then apply the model to manufacturing in Chile and Indonesia-two developing countries considering air pollution control strategies. We estimate substitutability in input demand in manufacturing-using standard techniques-and combine these with emission factors to assess the potential for emission reductions via demand changes. For sulphur oxides (SOx) and suspended particulates (TSP), emission elasticities with respect to the price of heavy fir!els range from -0.4 to -1.2. A price increase of 20 percent would reduce emissions of SOx, and TSP by 8 to 24 percent. While these results indicate how emissions can be reduced by presumptive taxes on fuels-clearing the air as well as the markets for energy-such a strategy preferably should be accompanied by other instruments that stimulate cleaner technologies. Similarly, emission standards should be accompanied by presumptive taxes on goods and inputs. Emission taxes, if feasible, optimally combine inducements along both avenues.