Thiamine status was assessed in healthy young and elderly subjects and institutionalized elderly patients by measuring dietary intake, erythrocyte levels of thiamine and the activity of the thiamine-dependent enzyme, erythrocyte transketolase, with and without the addition of excess thiamine pyrophosphate (the TPP effect). Healthy elderly subjects had a reduced intake of thiamine compared with the younger subjects but erythrocyte levels of thiamine and the TPP effect were comparable, suggesting adequate thiamine status. The institutionalized elderly patients had a low intake of thiamine compared with the healthy elderly as well as abnormal biochemical indices suggestive of suboptimal thiamine status. Thiamine deficiency does not appear to be a problem in healthy elderly people but those in institutions are at risk of deficiency which might adversely affect their clinical state.