Microbial diversity is essential for nutrient cycling and for biodegradation of the myriad substances that are introduced into soil. Previous research has shown that metal contamination can decrease the ability to degrade various common and rare substrates, but the relationship between species diversity and changes in substrate utilization patterns of microbial communities has not been examined. One of the best community-based approaches for indexing the functional diversity of soil microbial communities has been the use of substrate or metabolic fingerprinting, in which communities are screened for their ability to grow on various substrates in microtiter plates. In this study, we examined the effects of cadmium (Cd) on substrate versatility and metabolic redundancy in a soil having no prior exposure to heavy metals. Changes in substrate versatility were measured for 31 different substrates in microtiter plates amended with Cd at 0, 5, 10, 20, and 50 mg ml^-1. Results showed a linear decrease in substrate versatility and a decline in substrate utilization rates as Cd contamination increased. We analyzed 16S rDNA banding profiles generated by polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) of eubacterial communities that grew on 10 substrates. All Cd concentrations revealed a concomitant decrease in the number of 16S rDNA bands representing different species and groups of bacteria. The initial loss of sensitive species at 5 ppm Cd resulted in only a minor decrease of substrate utilization rates. At higher Cd concentrations, further decreases in species richness were substrate dependent, such that changes in substrate utilization rates were not necessarily correlated with microbial diversity. These findings suggest that communities comprised of metal tolerant species can degrade diverse substrates, and that substrate diversity assays alone may not be sufficient to assess fully the effects of heavy metal pollution on microbial communities. However, when substrate diversity assays are used in combination with 16S rDNA analyses of microbial species richness, it is possible to examine changes in microbial community structure and function with much greater precision. Thus, these combined methods are suggested as a new procedure for examining the response, adaptation, and resilience of soil microbial communities to heavy metal contamination.