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A number of mechanisms may be involved in the pathogenesis of thiamine deficiency in the alcoholic. Among these mechanisms are inadequate dietary intake of thiamine, impaired intestinal transport of the vitamin and decreased conversion of thiamine to the active coenzyme. The present study was undertaken to further investigate the mechanism by which alcohol can interfere with thiamine deficiency in the brain. Thus, the neurobehavioural development of rat pups (E) nursed by 12% ethanol/water-drinking mothers, or pups (E-T) nursed by mothers drinking 12% ethanol/water + thiamine hydrochloride mixture, was monitored from the 1st to 45th postnatal days. Appropriate pair-fed saccharose (S) and ad libitum controls (C) were assessed. Histological studies were performed at the age of 45 days on the hippocampal CA3 pyramidal neurons of the offspring from each treatment. Exposing rat pups to ethanol during pregnancy and lactation showed a significant impairment of neurobehavioural development, more cornered pyramidal cells in the hippocampal field CA3, reduced cell number and cell size. The results point out long-lasting effects of maternal alcohol exposure in the offspring. Both functional and structural studies showed that neurotoxic effects of developmental alcohol exposure were not reversed by thiamine administration. However, adverse effects of undernutrition following developmental alcohol exposure were suppressed by thiamine administration. From this work, we suggest that inadequate dietary intake of thiamine and impaired intestinal transport of the vitamin are not critical mechanisms leading to thiamine deficiency in chronic alcoholism. The most prevalent mechanism contributing to ethanol-induced thiamine deficiency in chronic alcoholics would be the alteration of thiamine metabolism, and particularly the reduction of the vitamin conversion to its metabolically active form TPP (thiamine pyrophosphate).