Serum pyridoxal (vitamin B6) concentrations were measured in 50 patients with significant diabetic neuropathy. There were 24 males and 26 females with a mean age of 58.2 years and a mean duration of diabetes of 9.8 years. The level of pyridoxal was significantly lower in these patients when compared with randomly selected diabetic patients matched for age and sex without clinical evidence of neuropathy. There was no significant difference in the duration of the diabetes between the two groups. The results indicate an association between pyridoxal deficiency and neuropathy in diabetic patients.