The microbial community composition of colonized cotton and leachate samples from a landfill was quantified using small subunit (SSU) rRNA probes (quantitative rRNA hybridization). Relative quantification of bacteria, eukaryotes, and archaea revealed variations in the landfill microbial community between samples from different areas of the landfill site and indicated the presence of potentially novel archaea. Anaerobic fungi were quantified in rumen fluid samples but were not sufficiently abundant for direct detection in the landfill samples.