Processes involved in the disposition of thiamine within the kidney were studied in rat kidney slices. Uptake of [14C]thiamine and its metabolism to [14C]thiamine phosphate were measured with and without the presence of ethanol. Whereas slice to medium ratios of 3.41 +/- 0.11 indicated uphill movement of [14C]thiamine, metabolism to [14C]thiamine phosphate provided a metabolic sink for movement of thiamine into the cell. Accumulation was saturable and associated, in part, with the formation of thiamine phosphate. Ethanol, at 25 mM, a concentration compatible with alcohol abuse, significantly (P < .001) decreased the maximal accumulation of [14C]thiamine from 210 +/- 12.7 to 115 +/- 4.2 nmol/g and the production of thiamine phosphate from 0.44 to 0.041 nmol/g. These data indicate a facilitated uptake of thiamine and a conversion to thiamine phosphate by the kidney. The effect of ethanol to decrease thiamine accumulation in kidney tissue is suggested to be at the phosphorylating step.