We investigated physical activity and its circadian rhythm as well as food and water intake in PVN-lesioned rats compared to those of VMH-lesioned rats. Body weight, food and water intake and ambulatory activity were recorded automatically on a microcomputer on the fourth day after creation of the PVN or VMH lesion. The weight gain in the PVN-lesioned rats was almost the same as that of the VMH-lesioned rats. The PVN-lesioned rats maintained the same circadian rhythm of eating and drinking as the controls. The ambulatory activity in the VMH-lesioned rats during the 24-h period was significantly less than the sham-operated rats, but that of the PVN-lesioned rats was almost the same as the sham-operated rats. The dominance of ambulatory activity in the dark period was observed in the PVN-lesioned rats as well as controls, in contrast to the VMH-lesioned rats, in which circadian rhythm was abolished. These results demonstrate that the PVN-lesioned obese rats show clear differences in physiological behavior from the VMH-lesioned rats.