Methionine metabolism was studied in a group of subjects having clinical signs and symptoms of peripheral neuropathy. Following a load of methionine, these subjects excreted higher amounts of cystathionine, and the ratio of cystathionine/ cysteine sulfinic acid was elevated suggesting a block in the conversion of cystathionine to cysteine sulfinic acid. The load return of methionine as cystathionine was significantly more. These results indicate that the activity of enzyme cystathionase, a pyridoxal-dependant enzyme, is low in pyridoxine deficiency. With pyridoxine therapy, there was a significant improvement in the clinical status, and the biochemical abnormalities were corrected.