An evaluation of the thiamine, riboflavin and pyridoxine (vitamin B1, B2 and B6) status of 60 patients with recurrent mouth ulcers was performed. Seventeen patients (28.2%) were found to be deficient in one or more of these vitamins. Replacement therapy of these vitamins was given to a study group of deficient patients and a non-deficient group for one month. At the end of therapy and after a follow-up period of 3 months, only those patients who had a B complex deficiency had a significant sustained clinical improvement in their mouth ulcers. Vitamin B1, B2 and B6 deficiencies should, therefore, be considered as another possible precipitating factor in recurrent aphthous ulceration.