Maternal alcoholism and thiamine deficiency are frequently considered to be the causal agents of the central nervous system (CNS) damage associated with mental retardation in the offspring. For further understanding of pathological mechanisms underlying CNS damage in both disorders, histological studies were undertaken in developing rats to compare the hippocampus CA3 pyramidal cells measurements and density between three patterns of thiamine deficiency and chronic alcohol exposure. Female rats were given thiamine-deficient diet during different periods of gestation and lactation to obtain pre-, peri-, and postnatal thiamine-deficient pups. Twelve percent ethanol/water drinking fluid was given to mothers throughout gestation and lactation to obtain ethanol-exposed pups. Thiamine was administered during developmental ethanol exposure to assess the extent of interference between ethanol and thiamine metabolism. Nondrug-treated dams were allowed ad lib access to food and water during gestation and lactation to yield control pups. Hippocampus histology was performed in 45-day-old rats, and the CA3 pyramidal cells measurements and density assessed and compared between all treatment groups. It appears that the mean nuclear size of pyramidal cells in the field CA3 was significantly reduced in all the treatments compared to the control. While the mean nuclear size decreased more severely in development ethanol exposure than in the three patterns of thiamine deficiency, no significant difference was noted when pre-, peri-, and postnatal thiamine-deficient rats were compared. However, thiamine administration during developmental ethanol exposure partially restored the mean nuclear size. In contrast, comparisons between ethanol-exposed pups and the three patterns of thiamine-deficient pups, exhibited similar intensity in the deficit of CA3 pyramidal cells. Cell loss generated by ethanol treatment was not suppressed by thiamine administration. Common and separate mechanisms underlying the effects of alcohol intoxication and thiamine deficiency on cell death and cell atrophy were suggested.