1. 1. One hundred and twenty intraspinal subarachnoid injections of synthetic vitamin B 1 in doses of 500 to 50,000 international units, (1 to 100 mg.) were given to twenty-eight patients, after preliminary experiments in cats. 2. 2. The cases treated were: inoperable cancer, 10; von Recklinghausen's disease, 1; multiple sclerosis, 2; degeneration of the pyramidal system of unknown etiology, 1; thromboangiitis obliterans with pregangrenous condition of feet, 1; duodenal ulcer with pulmonary tuberculosis, 1; alcoholic neuritis of the supraorbital nerve, 1, and of the sciatic nerve, 1; cardiac decompensation, uremia, anuria, 1; tabes dorsalis, 1; hypertrophic spondylitis, 2; osteoporosis of spine, 1; Paget's disease, 1; intractable pruritus ani and vulvae, 2; beriberi, 1; and acute poliomyelitis, 1. 3. 3. Natural or synthetic vitamin B 1 taken by mouth, rectum, subcutaneously, intramuscularly, or intravenously may not reach the nervous system because of digestion or neutralization by the alkaline intestinal contents, or neutralization by a general alkalosis, or because of barriers in diseased choroid plexuses. Even if vitamin B 1 does reach the cerebrospinal fluid, its action may be neutralized by the alkalinity of this fluid, which may be quite high as is so often found in cases of cancer and chronic illnesses. 4. 4. Given intraspinally, the beneficial effects appear much quicker than when given by other routes, because the vitamin remains in the cerebrospinal fluid for several days after a direct intraspinal injection. 5. 5. After intraspinal injection of vitamin B 1, improvement in varying degrees was noted in all cases. All felt better and looked better; appetites were increased, pain was lessened or abolished completely, muscular control improved, speech and gait improved, joints became looser, libido was increased, diplopia corrected. Some of the patients felt rejuvenated. 6. 6. The case of von Recklinghausen's disease (multiple neurofibromatosis) responded most favorably. Besides marked general improvement, some nodules became softer and smaller, and some have disappeared. The specific response to vitamin B 1 therapy suggests that the disease in this patient was due to a long-continued lack of vitamin B 1, together with an excessive amount of sweets in the diet. The possible relation of a chronic deficiency of vitamin B 1 to the cause of certain types of cancer is suggested. 7. 7. Many chronic or incurable conditions of the central and peripheral nervous systems may respond favorably to the intraspinal subarachnoid injection of synthetic vitamin B 1. It should prove of particular value in cases of multiple sclerosis, encephalitis, syphilis, and poliomyelitis. It should be tried in cancer cases, and whenever symptoms or signs of obscure origin fail to respond to usual methods of treatment. 8. 8. Treatment should start with ten milligrams, and be increased every fourth to seventh day, or more frequently in urgent cases. Injections should be given intraspinally in the lumbar region and thoroughly barbitaged with the spinal fluid. Doses over 20 mg. may cause slight elevation of temperature, weakness, stiffness of muscles and fingers, loss of appetite, buzzing or blowing in ears, and conjunctivitis lasting from several hours to several days. This is usually followed by signs of improvement. The maximum single safe dose intraspinally appears to be 100 mg. 9. 9. No patient developed any paralysis, anesthesia, or signs of meningitis following the intraspinal (subarachnoid) injection of vitamin B 1. Spinal fluid cell counts were not appreciably increased. The hydrogen ion reading of the spinal fluid was usually reduced. In all cases with a p h above 8.5, treatment should be pushed, but it is inadvisable to reduce the p h below 7.0, since restlessness and nervousness may ensue. Uncontrolled intraspinal administration may cause “vitamin B 1 poisoning,” which as demonstrated experimentally, may prove fatal. 10. 10. It is possible that synthetic vitamin B 1, when mixed with the cerebrospinal fluid, may leave the subarachnoid space via the perineural spaces of the cranial and spinal nerves. Preliminary observations point to a possible beneficial action of vitamin B 1 on diseased spinal cords and nerves when administered by injection into the subarachnoid space. 11. 11. Introduced into the subarachnoid space, synthetic vitamin B 1 stimulates the sympathetic nervous system. 12. 12. Synthetic vitamin B 1 is a remarkable specific oxidative and catalytic drug of great benefit to injured, diseased, or avitaminotic nerve tissue. 13. 13. Synthetic vitamin B 1 intraspinally has a powerful rejuvenating action unknown to any other drug, and is one of the most valuable therapeutic agents at our command.