The design of field studies investigating the effects of air pollution on forest ecosystems is discussed with an emphasis on the use of permanent plots along exposure gradients. Results from the Michigan gradient study in the United States are summarized. In general, there has been no detectable loss in aboveground productivity but there have been very clear changes in the cycling of mineral elements in the ecosystems due to acidic inputs. Exposure levels in central and eastern Europe are much greater than those in the United States and this provides an opportunity for scientists in both countires to effectively extend their gradient studies through cooperative efforts. Specific areas of cooperation that are being initiated with Polish scientists are summarized.