A pollution minimization methodology was developed for chemical process design using computer simulation. It is based on a pollution balance that at steady state is used to define a pollution index with units of mass of pollution per mass of products. The pollution balance has been modified by weighing the mass flowrate of each pollutant by its potential environmental impact score. This converts the mass balance into an environmental impact balance. This balance defines an impact index with units of environmental impact per mass of products. The impact index measures the potential environmental effects of process wastes. Three different schemes for chemical ranking were considered : (i) no ranking, (ii) simple ranking from 0 to 3, and (iii) ranking by a scientifically derived measure : of human health and environmental effects. Use of the methodology is illustrated with two examples from the production of (i) methyl ethyl ketone and (ii) synthetic ammonia.