OBJECTIVE To explore the primary regularity of cerebral electrical impedance (CEI) change in healthy people, patients with intracerebral hemorrhage (ICH) and patients with cerebral infarction (CI). METHODS CEI of 200 healthy volunteers, 78 patients with ICH and 51 patients with CI were measured by noninvasive brain-edema monitor. The results of perturbative index (PI) converted from CEI were compared with the volumes of infarction, hematoma and surrounding edema, which were calculated by image analysing system according to MRI or CT scan. RESULTS (1) In the normal groups, PI in the left and right sides of cerebral hemispheres was respectively 7.98 +/- 0.95 and 8.02 +/- 0.71, and there was no significant difference between the two sides (p>0.05). (2) In the patients with ICH, PI of the hematoma side initially was lower than the other side, but then increased and finally exceeded that of the other side. The average transitional time was 19.67 +/- 11.52 hours. Perturbative index of the hematoma side after the transitional time was much higher than before the transitional time in the same patients (7.79 +/- 0.75 versus 7.09 +/- 0.72) (p<0.001). The volumes of peri-hematoma edema were also significantly larger after the transitional time than before (24.32 +/- 12.86 versus 13.33 +/- 6.12) (p<0.05). There was a positive correlation between the PI of hematoma side and the volumes of peri-hematoma edema (p<0.01). (3) In the patients with arterothrombotic cerebral infarction, PI in the infarct side was higher than that in the opposite side 3-5 days after onset (8.93 +/- 1.89 versus 8.58 +/- 1.61) (p<0.001), and PI of the infarct side had a positive correlation with the volume of infarction (p<0.001). (4) The sensitivity of PI was high when the volumes of lesions were >20 ml or the position of them were located in the basal ganglia, but was low when the volumes were <20 ml or the position near the midline. CONCLUSIONS CEI may be a useful parameter for noninvasively monitoring the change of brain edema and hematoma in stroke at bedside. It could be a good complement to CT and MRI.