[en] To date, clinical experiments with high LET irradiation have used fast neutrons, π-mesons, and heavy ions. The data for all of these modalities will be reviewed here, but by far the greatest body of information is for fast neutrons. Boron neutron capture therapy work for brain tumors, and interesting area in its own right, will not be discussed. In the paper, the author considered separately the brain and the spinal cord in terms of radiation effects. Most of the information on the brain comes from the treatment of high-grade gliomas and so the effects of the tumor and its surrounding edema must be folded in. There is, however, some information relating to the treatment of tumors lying adjacent to the brain. The spinal cord data come primarily from the treatment of head and neck tumors and intrathoracic tumors. Because the majority of these tumors were quite advanced, they often caused the patient's early death, and many patients may not have survived long enough to show the effects of radiation damage even if doses were given that exceeded cord tolerance