In this microcosm study we have monitored the performances of 12 butane-utilizing consortia during a long-term aerobic cometabolic degradation of chloroform (CF). After approximately 100 days of continuous CF depletion, a sudden improvement of the biodegradative performances (7-fold increase of chloroform degradation rate) was observed in two microcosms in which the highest amount of depleted CF (> 70 mg / kg of dry soil) was observed. Two bacterial strains, isolated from the CF-degrading microcosms, were identified as belonging to the genera Rhodococcus and Stenotrophomonas, respectively. A strain, named F, was further characterized to establish the involvement of the butane-monooxygenase in CF degradation.