The impact of transcranial pulsed magnetic stimulation on blood-brain barrier permeability was studied in rats. An integral uptake technique was used to asses the blood-brain barrier permeability to the tracers [3H]sucrose, [14C]urea, and 36Cl-. From the arterial plasma concentration-time curve-integral the permeability surface-area products were calculated. A Dantec magnetic stimulator delivering a peak magnetic field of 1.9 T with a rise-time of 160 microseconds was used for transcranial stimulation of the rats. One group of rats had about 50-60 stimulations during the 15-min infusion of the tracers while another group was exposed to 50 magnetic stimulations a day for one week. A third group comprised the controls. No differences in permeability surface-area product were found for any of the three tracers in the rats exposed to magnetic stimulation as compared with the controls. It is concluded that with regard to blood-barrier integrity, pulsed magnetic stimulation of the brain can be regarded as safe.