Thiamine status of 196 institutionalised (in hospital, residential accommodation and sheltered dwelling) and non-institutionalised Caucasian aged subjects was assessed by combined dietary, biochemical and clinical studies. Fourteen subjects (7.1 per cent) consumed less than two-thirds of recommended vitamin B1/DAY. Erythrocyte transketolas activity coefficient (a) test indicated biochemical deficiency of thiamine in 17.6 per cent males and 12.5 per cent females. The incidence of deficiency was highest in subjects of sheltered dwelling. Multivitamin supplementation failed to raise the biochemical thiamine status to normal in 2.9 per cent subjects. No characteristic clinical features of thiamine deficiency were noted, though extreme loss of appetite was reported by 3 subject with activity coefficient greater than 1.30. Dietary intake was not always associated with deficient biochemical indices. The possible factors such as alcohol intake and low folate status affecting the biochemical status of thiamine are discussed.