The sensitivity of electricity consumption to air temperature and air humidity are effective indicators in evaluating the impacts of countermeasures against urban heat islands. The impacts of these countermeasures vary in time and space and so sensitivities based on finer resolution data are needed. Using actual hourly electric power consumption data from the business districts of Tokyo, we calculated the sensitivity of electric power consumption using multiple regression analysis. The sensitivities appear from 07:00 to 23:00 local standard time (LST) during weekdays during both winter and summer, mainly from 09:00 to 17:00 LST. The sensitivities to air temperature during winter are approximately 0.7-1.1 (W/floor-m(2))/degrees C on an average and those during summer are approximately 1.1-1.4 on an average; the sensitivities to air humidity are approximately 0.6-0.9 on an average. It was found that the sensitivities to air temperature are caused due to heating during winter and cooling during summer; further, the sensitivities to air humidity were caused by dehumidification not for conditioning the air humidity of the room but for the condensation around the air-conditioner's coils with cooling during summer. (c) 2008 Elsevier Ltd. All rights reserved.