Investigations of the influence of Pb on soil microbial communities have focused on Pb concentrations of 1 g kg-’ or less (Barkay et al., 1985; Capone et al., 1983; Chang and Broadbent, 1981; Doelman and Haanstra, 1979; Trevors et al., 1985). However, a number of environments exist in which Pb concentrations exceed 1 g kg-’ dry soil (Davenport and Peryea, 1991; Davis et al., 1992; Bisessar, 1982). Bisessar (1982) reported an inverse correlation between Pb concentration and the bacterial population size in soil near a secondary lead smelter. However, similar trends in the concentrations of Pb, As, Cd, and Cu at the site make it difficult to attribute the reductions in population size to Pb alone. Although the effects on microbial carbon mineralization of Pb concentrations as high as 20,000 g kg-’ dry soil were investigated by Debosz et a/. (1985), differences in pH between Pb treatments and the lack of controls for abiotic CO, evolution make the results of the study equivocal. Our purpose was to examine the effects of g kg-’ Pb concentrations on the growth and productivity of soil microbial communities.