The addition of nonindigenous microorganisms to soil can alter the structure of the soil foodweb and, consequently, the manner in which nutrients cycle through soil. Alterations in the cycling of nutrients through soil may, in turn, affect the growth, reproduction, and competitive ability of the vegetative community. To assess the effectsof introduced organisms on soil foodwbs, a xeric soil was amended with 500 μg g−1 of the herbicide 2,4-D and inoculated with either the genetically engineered organisms (GEM) Pseudomonas putida PP0301(pRO103) or P. putida PP0301 (the wild-type strain), as well as controls where no 2,4-D was added. Plasmid pRO103 contains constitutively expressed genes that encode for the mineralization of phenoxyacetate and the partial degradation of 2,4-D. Soil for this study was collected from the same site as the soil used in previous studies, but was not amended with glucose. Degradation of 2,4-D was not detected during the course of this study, although isolates of P. putida PPO301(pRO103) obtained from soil amended with 2,4-D at the end of of the study were able to catabolize phenoxyacetate in pure culture, suggesting that they retained the constitutive pathway for the partial degradation of 2,4-D. In all treatments amended with 2,4-D (with or without added PP0301(pRO103) or PP0301), active fungal biomass, active bacterial biomass, plate count estimates of bacteria, numbers of nitrifying bacteria, and numbers of flagellates and amoebae decreased. In soil without 2,4-D treatment and inoculated with the GEM, PP0301(pRO103) , active fungal biomass and total fungal biomass was reduced relative to that inoculated with PP0301. Increases in protozoan biomass were clearly evident in unamended soil inoculated with either PP0301(pRO103) or PP0301. The GEM had no continuing effects on the structure and function of the soil foodweb relative to the wild-type strain, in contrast to previous studies where 2,4-D was degraded and the fungal community was affected throughout the experiment.