We clarified that etoposide (VP-16), a topoisomerase II inhibitor, induced apoptosis in the mouse fetal brain. Apoptotic mechanisms and cell cycle arrest in this system were investigated. Four mg/kg of VP-16 was injected into pregnant mice on day 12 of gestation (GD12). The cell cycle and expression of protein and mRNA of p53 and its transcriptional target genes were examined in the fetal brain. The number of p53- and p21-protein-positive cells peaked at 4 h after treatment (HAT). The expression of p21 mRNA was significantly increased at 4 HAT and 8 HAT. The expression of fas mRNA was significantly increased from 2 to 12 HAT. Significant expression of puma mRNA was observed from 1 HAT to 48 HAT. Flow cytometric analysis revealed that VP-16 induced S-phase accumulation and G2 arrest at 4 and 8 HAT, and VP-16-induced apoptosis was significantly increased from 4 to 24 HAT. In an experiment using BrdU treatment of pregnant mice, the migration of neuroepithelial cells in the fetuses was delayed as compared to the migration of controls, and BrdU-positive signals were observed in some pyknotic cells from 8 to 12 HAT. The present results suggest that VP-16 might induce cell cycle arrest at G2/M phase and apoptosis in a p53-related manner.