Fetal alcohol syndrome (FAS) is now well documented, but factors that affect the severity of the accompanying central nervous system damage are still not well understood. In a series of experiments, artificially reared neonatal rats were exposed to alcohol during postnatal days 4-10 (during the brain growth spurt of the rat) to evaluate the consequences of various patterns of alcohol consumption in contributing to the severity of alcohol-related brain damage. In the first experiment, groups of rat pups were given different doses of alcohol (6.6 to 9.8 g/kg) in a milk formula in eight 15-min feedings over each 24 hr. Measures of brain weight on day 10 indicated an inverse relationship between dose and brain weight. Re-evaluating the results with respect to blood alcohol concentration (BAC) revealed an even stronger correlation between BAC and microencephaly. A series of experiments followed in which various doses of alcohol were condensed into fewer and fewer hours each day. Condensing the dose produced higher BACs for a given dose and produced more severe microencephaly, greater neuronal loss, behavioral hyperactivity and impaired spatial navigation. Some of these effects were permanent with females more affected than males on some measures. These data suggest that patterns of alcohol consumption that produce high BACs, such as binge drinking, may be especially harmful to the brain of the developing fetus.