Female mice were treated with 0 or 8 mg/kg chlordane daily for 18 days during pregnancy. The fetuses of these mice were assayed for fetal liver hematopoietic activity at 18 days gestational age. Hematopoietic activity was evaluated for in vitro granulocyte-macrophage colony-forming units (GM-CFU) and in vivo spleen CFU (CFU-S). The consistent finding was a significant depression of the numbers of both fetal liver GM-CFU and CFU-S without a change in liver cellularity in fetuses exposed to 8 mg/kg chlordane. These data show that the damage to stem cells that persists into adult life as a result of chlordane exposure, as reported earlier by Barnett et al. (1990) Fundam. Appl. Toxicol. 14, 688-695, occurred during the fetal period.