Epicuticular waxes of trembling aspen (Populus tremuloides M i c h x.) clones differing in O3 tolerance were examined for three growing seasons (1995-1997) at three localities (Rhinelander, Wisconsin-clean and control site; Kalamazoo, Michigan-moderate pollution loading and Kenosha, Wisconsin-high pollution loading) in the Lake States region of the USA. Statistical difference was found in the concentration of Al, As, Ca, Cd, Cu, Fe, Mn, N, Ni, P, Pb, S, and Zn in the aspen foliage. Particulates on the leaves surfaces and in the stomata at the three sites include Al, Ca, Fe, Si, Mg, Na, S, Th, Ti and Y. These elements are typical for particles from industrial sources. Fungi effect was observed on leaves from all localities. Differences in epicuticular wax structure, as determined by scanning electron microscopy were found between these sites with the most severe impact being found at the Kenosha site. These include severe erosion of waxes, and occlusion of stomata. The results suggest that O3 pollution of the Kenosha and Kalamazoo site show significant negative impact on epicuticular waxes of aspen and that these impacts are the most severe on the O3 sensitive clones.