There is increasing evidence for the role of thiamine deficiency in ethanol neurotoxicity and in development of alcoholic organic brain disorders other than Wernicke-Korsakoff syndrome [WKS] and cerebellar degeneration. Investigations in humans and in animal models have implicated a reduction in the activities of thiamine-utilizing enzymes as the metabolic basis of tissue injury due to thiamine deficiency. We have investigated the interactions of the thiamine-utilizing enzyme transketolase [Tk], derived from human fibroblasts, lymphoblasts, and various brain regions, with its cofactor, thiamine pyrophosphate [TPP], in an attempt to elucidate the molecular basis of selective brain damage in alcoholism-associated thiamine deficiency. There were no significant differences in the isoelectric pattern of Tk among the nine brain regions (white matter and grey matter) examined. However, Tk activity/mg protein, increase in Tk activity with addition of excess TPP (TPP effect), and TPP-dependent rate of formation of active Tk holoenzyme (tau) varied 2.5-, 6-, and 4-fold, respectively, among these brain regions. These differences in tissue requirements for TPP may contribute to the selective vulnerability of certain brain regions to alcoholism-associated thiamine deficiency, and may influence the pattern of clinical impairment in the individual patient.