The wood of nine trees of Cecropia glazioui Sneth. from three different areas of Serra do Mar in Sao Paulo was quantitatively analysed. One of the areas is highly polluted by petrochemical, chemical, fertilizer and steel industries, another has hardly any pollution, and a third one was intermediate. The modifications found in samples of the most polluted region were in general in agreement with those present in woods from unfavourable environments, such as water-stressed sites. Since the water is not a limiting factor in the area, pollution is believed to be responsible for the modified wood structure.