We believe that SIP has the potential for wide application in microbial ecology. It offers a cultivation-independent means of investigating the effect of changes in environmental conditions, including temperature, water potential, pH and substrate concentrations, on the taxonomic identity of functionally active groups of microorganisms. This ability to link function with taxonomic identity may also assist in the formulation of isolation strategies for microorganisms that are actively involved in ecologically important processes. With an ever-increasing range of 13C-enriched substrates becoming available, and the potential of using 15N- and 2H-enriched compounds, it will be possible to use SIP to identify many microorganisms involved in the cycling of carbon and nitrogen in the environment.