Many conditions in clinical neurology may be responsive to pyridoxine as a therapeutic agent. The current difficulty is in trying to isolate the conditions that are most likely to respond. Treating seizures is a major part of a neurologic practice. Our current therapeutic agents are only partially successful and limited by multiple side effects. One problem is that patients often have to take these agents for an entire lifetime, further raising the risk of toxicity. If pyridoxine supplementation can improve the efficacy of currently used medications, it will be gladly accepted into our therapeutic arsenal. Headache, chronic pain, and depression all appear to run together in many of our patients. The observations that serotonin deficiency is a common thread between them and that pyridoxine can raise serotonin levels open a wide range of therapeutic options. Small studies have been carried out with mixed success. Comparison with amitriptyline in the treatment of headache appears to show about equal efficacy, although side effects would be expected to be more of a problem with the amitriptyline. Behavioral disorders are relatively common and continue to be a major problem, disrupting the lives of the patients and their families. Current treatments are not acceptable to most people because of the risk of side effects with long-term usage. If, as Dr. Feingold suggests, many of these problems are caused by "toxic" exposures to chemicals that are pyridoxine antagonists, supplementation at early ages may reduce the incidence of hyperactivity and aggressive behavior. This raises the question of safety. Is pyridoxine safe for long-term use in large segments of the population, including children? The studies on children with Down's syndrome and autism, utilizing much higher doses than are used for other therapeutic purposes, seem to indicate relative safety if carefully monitored. Studies involving large population groups with carpal tunnel syndrome, all adults, using 100-150 mg/day have shown minimal or no toxicity in five- to 10-year studies. Women self-medicating for PMS taking 500 to 5000 mg/day have shown peripheral neuropathy within one to three years. It would appear from this retrospective analysis that pyridoxine is safe at doses of 100 mg/day or less in adults. In children there is not enough data to make any sort of suggestion. Because the major neurologic complication is a peripheral neuropathy and the causes of this condition are myriad, pyridoxine may cause neuropathy only in patients with a pre-existing susceptibility to this condition.