The effect of electrically induced convulsions upon the permeability of the blood-brain barrier to trypan blue was studied in 67 rats. A sequence of 12 electroshocks over a period of 30 days, 24 hours or 3 hours were produced with the Spiegel's corneal electrodes and a stimulator. The permeability study of the blood-brain barrier was performed through the gross and microscopic anatomical examinations of the central nervous system of animals injected with trypan blue, supravital dye, which normaly does not get through the blood-brain barrier and thus does not stain the brain. It was verified that only the pineal body and the meninges have been stained in both treated and non-treated electrochocked groups. The stain intensity of the pineal body was proportional to the duration of the dye in the vascular space (one, two or three hours). Nevertheless staining of the central nervous system was observed when the dye was injected before the animals had been subjected to 12 electroshocks/3 hours. The results of the present study suggest that the increase in permeability of the blood-brain barrier to trypan blue, in rats treated with repeated electrically induced convulsions, persists only for short periods of time. It is possible that the increased permeability is related to increased neuronal activity during electroshocks.