In some patients without vitamin B6 deficiency, epilepsy can not be controlled without an extra supplement of vitamin B6. The therapeutic role of pyridoxal phosphate (PLP), the active form of vitamin B6, may not be replaced with other forms of vitamin B6 sometimes. Until now, four inborn errors of metabolism are known to affect vitamin B6 concentrations in the brain. Three of them are hyperprolinemia type 2, antiquitin deficiency, and pyridoxine phosphate oxidase deficiency. The fourth disorder occurs in neonates with hypophosphatasia and congenital rickets. All patients with these conditions present with early-onset epilepsy that is resistant to conventional antiepileptic medications. Patients with three of the conditions respond to any form of vitamin B6. Only those with pyridoxine phosphate oxidase deficiency respond to PLP instead of pyridoxine. Interestingly, the authors have successfully treated many patients without the above four disorders using vitamin B6, and have found that the treatment was more effective with PLP than with pyridoxine, though the mechanism is not known. Since PLP is as inexpensive as pyridoxine, we suggest replacing PLP for pyridoxine when treating children with epilepsy.