Maternal heroin abuse has been shown to result in teratogenic neurobehavioral defects in the offspring, but the underlying mechanisms remain largely unknown. This study was designed to explore the role of neuronal apoptosis in the heroin-induced neurobehavioral defects of learning and memory. Pregnant BALB/c mice were treated with either heroin or saline. The animals in the heroin group received heroin subcutaneously at a dosage of 10 mg/kg/day on embryonic days (E) 9-18, while those in the saline group were treated as drug-naive. Offspring were grouped as prenatal heroin exposure (HER), prenatal saline exposure (SAL), and control (CON) groups, according to the maternal treatment regimen. Some of the mice were killed and their hippocampus harvested on postnatal day (P) 14, and the tissue subjected to reverse transcription polymerase chain reaction, Western blotting, and immunohistochemistry to reveal the mRNA and protein expressions of caspase-3, Bcl-2, and Bax. The Morris water maze was applied to assess the learning and memory capability of the mice at P30; poor maze performances were observed for the animals in the HER group. The results also showed that the mRNA and protein expressions of caspase-3 and Bax were significantly increased, while that of Bcl-2 was markedly decreased in the HER group compared with both the SAL and CON groups. The immunohistochemistry revealed significant caspase-3 immunoreactivity in the dentate gyrus and cornu ammonis (CA) 1 subareas of the hippocampal formation, whereas, no significant changes were seen in subarea CA3. These findings suggest that prenatal heroin exposure during the E9-18 period enhances neuronal apoptosis by altering the expressions of caspase-3, Bcl-2, and Bax in the mouse hippocampus, and leads to impairment in hippocampus-dependent learning and memory. © 2009 IBRO.