Air pollutants modify the productivity of agrisystems. Any effect of air pollution on growth or quality of a plant is an effect of productivity. Early efforts to estimate the effects of air pollutants on crop productivity were often based only on observation. Of the different methods utilized to determine losses of crop productivity, the open-top field chambers are perhaps the best for determining effects on plant yield, at least for 03. Several studies have been conducted to determine the effects of photochemical oxidants from major metropolitan areas on productivity in natural ecosystems. The controversies associated with the effects of air pollution on plants in general, and ecosystems in particular, extend to the possibility that pollutants alter the relationship between plants and destructive insects and kill beneficial insects, or that accumulation in insects makes them a vehicle for their transfer in ecosystems. (Copyright (c) 1981 by Annual Reviews Inc.)