Another method of monitoring microbial activity with GeoChip is to combine it with SIP (Leigh et al., 2007) . Microcosms were set up from soil samples collected from the root zone of a tree growing in a PCB-contaminated site and fed 13 C-labeled or unlabeled biphenyl. Genes involved in biphenyl degradation were detected as were other organic contaminant degradation genes including those for degradation of benzoate, catechol, naphthalene, and phenol.