The effects of etoposide on the death of neurons cultured from the central nervous system (CNS) of fetal rats were examined. The cultured neurons died in the presence of 1-40 micrograms/ml of etoposide, which is known to induce programmed death in some kinds of cells, and this cytotoxic effect was prevented by inhibition of protein synthesis and/or RNA synthesis. Furthermore, DNA degradation, including a ladder-like pattern, became evident in these neurons 3 h after incubation with etoposide (10 micrograms/ml), whereas cell death commenced after about 6 h. These results indicate that etoposide-treated CNS neurons require new protein and RNA synthesis to undergo an active death programme, and that internucleosomal fragmentation of DNA mediates the etoposide-induced programmed cell death. This culture system of etoposide-treated CNS neurons is thought to be a useful model for the study of programmed neuronal cell death.