In two earlier papers1the writer has described a method by which it is possible to demonstrate spinal subarachnoid block in cases of compression of the spinal cord and other conditions which obstruct the free interchange of fluid within the spinal subarachnoid space. The object of the present short communication is to review briefly the results of this method after nearly four years of clinical use, in order to form some estimate as to its value. The method employed has remained unchanged with certain modifications. It depends on (1) a careful manometric study of the fluid, by means of double and at times of triple puncture of the subarachnoid space, and (2) comparison of the fluids obtained at two or more loci. For the hydrodynamic studies the points of puncture are designed to be above and below the obstruction, and therefore needles are not necessarily inserted at the same