The distribution of cocaine and the cocaine metabolite benzoylecgonine (BE) in brain and plasma of Sprague-Dawley rat dams and their near-term fetuses was assessed 0.5 and 2 h post-injection on gestational day 20 following chronic daily subcutaneous injections of 10, 20, or 40 mg/kg/3 ml cocaine hydrochloride beginning on gestational day 8. Plasma concentrations of cocaine reached in the dams were found to be in the range of, or to exceed, those reported in human cocaine users. Dose-related increases in plasma and brain levels of cocaine in the dams and the fetuses were observed, particularly at 2 h post-injection. Fetal concentrations of cocaine in brain and plasma were approximately 2-3-fold less than those of the dams, suggesting that the placenta may somewhat restrict cocaine entry into fetal circulation. Brain/plasma cocaine ratios, however, were generally equivalent in the dams and fetuses, suggesting that once cocaine enters the circulation, its affinity for brain tissue is similar in the fetus and dam. Whereas plasma levels of BE, like cocaine levels per se, were greater in the dams than fetuses, BE concentrations in fetal brain were greater than those observed in maternal brain. These high levels of BE may contribute to the production of neurobehavioral alterations in cocaine-exposed offspring, given that this active cocaine metabolite has been shown to form molecular complexes with calcium ions (Misra and Mule 1975), thereby having the potential to influence a multiplicity of calcium-regulated developmental events.(ABSTRACT TRUNCATED AT 250 WORDS)