There has been growing concern over human exposure to adenoviruses through drinking water due to the extreme resistance of human adenoviruses to the traditional UV technology (low-pressure (LP) UV). As an effort to develop an effective treatment strategy against human adenoviruses in drinking water, we determined the effectiveness of sequential disinfection with an alternative UV technology (medium-pressure (MP) UV) and free chlorine. Human adenovirus 2 (Ad2) was irradiated with a low dose of MP UV irradiation (10 mJ/cm(2)) through UV collimated apparatus and then exposed to a low dose of free chlorine (0.17 mg/L) at pH 8 and 5°C using a bench-scale chemical disinfection system. A significant inactivation (e.g. 4 log(10)) of Ad2 was achieved with the low doses of MP UV and free chlorine within a very short contact time (∼1.5 min) although there was no apparent synergistic effect on Ad2 between MP UV and free chlorine. Overall, it is likely that the sequential disinfection with UV irradiation and free chlorine should control the contamination of drinking water by human adenoviruses within practical doses of UV and free chlorine typically used in drinking water treatment processes.