Offspring of C57BL/6J mice injected daily with phenobarbital (20 or 40 mg/kg) for the last 6 or 7 days of pregnancy were compared with offspring of saline control mice on behavioral and neurochemical measures of brain function at 21 days of age. Activity in an open field arena was elevated in male offspring and reactivity to presentation of a tone-light stimulus was increased for female offspring of drug treated dams. Brain concentration of dopamine and norepinephrine was reduced and the uptake of dopamine, norepinephrine serotonin and gamma-aminobutyric acid into synaptosomal preparations of brain tissue was greater for treated offspring. Both the behavioral and neurochemical indices indicate that the brain is altered by maternal prenatal injections of phenobarbital but the relationship between these changes remains speculative.