No final conclusion has yet been achieved on whether the area postrema (AP) is involved in the regulation of cardiovascular activity in the rats. The aim of the present study was to investigate the role of the AP in the regulation of basal blood pressure under normal as well as abnormal (cold stress) conditions in Sprague-Dawley rats. The lesion of AP was performed by the electrolytic-lesion method. Stressed animals were subjected to chronic intermittent cold stress (2 degrees C, 3 h/day for 14 days). The systolic blood pressure was measured by the indirect tail-cuff transducer method. The results showed that no significant difference was found between systolic blood pressure measured before and after AP-lesion surgery. The AP-lesion group had similar systolic blood pressure to both sham-operation and the control groups under normal environmental conditions. However, it was found that cold stress resulted in a significant increase in systolic blood pressure in the AP-lesion rats, but not in sham-lesion animals, within two weeks. Furthermore, there was no significant difference between blood pressures of sham-lesion rats with or without cold stress and the control animals. These results support the view that the AP plays no role in keeping basal blood pressure under normal condition and indicate as well that the AP is important in maintaining normal blood pressure under the conditions of stress (cold).