Effects of anticonvulsant treatment and low levels of folate and thiamine on amine metabolites in cerebrospinal fluid. A total of 157 epileptic patients were studied with respect to (1) biogenic amine precursors and metabolites in the CSF, (2) levels of folate and thiamine in the blood and CSF, (3) length of treatment with phenytoin (PHT), (4) PHT intoxication, (5) CNS atrophy. Alterations in CSF amine metabolite levels were related primarily to PHT intoxication, and low CSF folate and thiamine levels, but not to length of treatment or CNS atrophy. PHT intoxication increased CSF 5-hydroxyindoleacetic acid (5HIAA). Low folate levels were associated with decreased CSF 5HIAA and homovanillic acid, while low thiamine levels were associated with decreased CSF 5HIAA and 3-methyoxy-4-hydroxyphenylethylene glycol. It remains to be seen to what extent these alterations in biogenic amine metabolism, mediated by low CNS vitamin levels, also lead to deficits in cerebral function. 