Recently, new methods for monitoring specific bacterial populations in environmental samples have become available. These methods employ the techniques of molecular biology to distinguish, enumerate and monitor individual bacterial populations within a microbial community by the detection of DNA sequences specific to those populations using appropriate molecular probes. DNA-based detection of bacterial populations helps to overcome a major limitation of microbial ecology and soil microbiology; the difficult task of specifically monitoring an individual population of microbes in the environment, and in the presence of the entire microbial community. Such capabilities are essential to understanding the complex interactions between the environment, other microorganisms and the population(s) of interest.