The effects of acid precipitation and ozone on the composition of the ectomycorrhizal community of red spruce saplings were evaluated. In 1986, saplings were excavated from a site in Maine that had been clear-cut in 1979. Saplings were then potted in native soil and transported to Ithaca, New York. With the exception of an ambient control treatment, trees were grown in open-top chambers. Saplings were exposed to five levels of ozone and three levels of acid precipitation beginning in July 1987. Ectomycorrhizae were sampled in 1988 and 1991 after one and four years of treatment, respectively. Although the percentage of root tips infected by ectomycorrhizal fungi was not affected by treatments, a shift in the composition of the ectomycorrhizal community occurred in response to acid precipitation treatments for both sampling years. Among the seven ectomycorrhizal morphotypes identified, the percent composition of one morphotype increased and another decreased in response to higher rain acidity. Alone, ozone treatments did not influence ectomycorrhizal composition; however, a significant interactive response to ozone and acid precipitation was observed in the organic soil horizon in 1988. Such shifts in the composition of the ectomycorrhizal community may indicate that the experimental trees were stressed by pollution treatments.