The aim of this study was to determine the mechanism of transport of (14)C-thiamine in the hearts of healthy (nonalcoholic) and chronically alcoholic guinea pigs. We used the single-pass, paired-tracer dilution method on isolated and retrogradely perfused guinea pig hearts. The maximal cellular uptake (U(max)) and total cellular uptake (U(tot)) of (14)C-thiamine were determined under control conditions and under influence of possible modifiers. We tested how the presence of unlabeled thiamine, metabolic inhibitors, or absence of sodium ions influence the transport of (14)C-thiamine. The results of our experiments show that the transport of (14)C-thiamine is specific and energy-dependent and that its properties are significantly changed under the influence of chronic alcoholism. The latter effect occurs by increase in both U(max) and U(tot), as a manifestation of a compensatory mechanism in thiamine deficiency.