The pathway by which barbital reaches the brain is still unknown. Generally there are two possible pathways through which substances in blood enter into the brain, namely, one, directly through blood vessels and the other, by way of the choriomeningeal plexus. Barbital will possibly enter the brain by the former pathway but it may enter the brain by way of the cerebro-spinal fluid as in the case of P.(32) In order to verify this point, I have measured the barbital concentrations in the lumbar fluid and the ventricle fluid, each obtained at the time of lobotomy and at the pneumo-ventriclography, respectively. From these results, it has been found that barbital immigrated into the cerebro-spinal fluid faster than bromine so that there seems to be a possible pathway to the brain through this fluid. Moreover, in the measurements of the barbital concentration in the ventricle fluid after oral administration has been found higher than that in the lumbar fluid. For this reason, I believe that the choriomeningeal plexus plays the leading rôle in the production of the cerebro-spinal fluid as contended by other investigators.