Established methods for measuring a broad spectrum of microbial activities were evaluated for their ability to detect perturbations of the soil environment by introduced microorganisms. These methods included: gross metabolic activity and carbon mineralization, as measured by respiration (CO2 evolution); activity of selected enzymes (arylsulfatases, acid and alkaline phosphatases, dehydrogenases); and indicators of the community structure of the indigenous microbiota (species diversity, physiological groups, antibiotic-resistance profiles). The evaluation of these variables, as well as the fate of the introduced microorganisms (Escherichia coli W3110 (R702) and its homologous, plasmidless, parental strain, W3110), was conducted over a 33-day period. Statistically significant differences only in some components of the microbiota were detected between soil inoculated with W3110 (R702) or W3110 of not inoculated. However, these differences were transient and, therefore, probably not ecologically significant.