Blood vitamin status (B1, B2 and B6) was assessed by erythrocytic enzyme activation tests in 7 male and 1 female chronic alcoholics (mean age (±s.d.), 43·12 (13·7) years; range, 25-64 years) on admission and 6 hr later on the same day after oral administration of a single dose of polyvitamin. Seven out of 8 patients were found to be deficient in vitamin B1, 5 in B6 and none in B2. But after single-dose oral therapy, tendency to improvement of blood vitamin status was clearly evident in all patients. It is therefore suggested that a subgroup of chronic alcoholics may benefit from oral supplementation of vitamins. Clinical implications of vitamin deficiency in chronic alcoholics are briefly discussed.