The asymmetrical breakdown of the blood-brain barrier to Evans-blue was studied in female rats subjected to pentylenetetrazol induced seizures. The animals were divided into two groups: control group (Group I): eight female rats were injected with 0.2 mi of saline into the femoral vein. Pentylenetetrazol (PTZ) group (Group TT): twelve female rats were injected 80 mg/kg PTZ (i.v.). The amount of release dye in homogenized cerebral hemispheres was determined by spectrophotometric analysis. The mean value for Evans-blue dye was found to be 1.81 +/- 0.5 mg% in the left hemisphere and 1.40 +/- 0.4 mg% in the right hemisphere after PTZ induced seizures. This difference betwen left and right hemispheres was found to be significant (p < 0.05). The findings suggest that disruption of the blood-brain barrier during PTZ induced seizures is asymmetric between right and left hemispheres.