Experiment 1. Chick embryos received a single DFP exposure (0, 50, 100, 200, 400, 800, 1600, 3200 [mu]g/kg) on embryogenesis day (E) 11. DFP was fatal to all embryos at 400 [mu]g/kg and above, but did not affect hatch success at lower doses. Prenatal DFP reduced hatch weight and increased weight by posthatch day (PHD) 14. Prenatal DFP produced sex- and dose-dependent changes in distress vocalizations (DVs), but not activity on PHD 1. DFP increased tonic immobility duration (TI) on PHD 14. DFP increased lipopolysaccharide-induced lymphocyte proliferation in blood harvested on PHD 16 in females;Experiment 2. Daily DFP (0, 50, 100, or 200 [mu]g/kg) on E 10-12 reduced hatch success. DFP reduced hatch weights in males, but not females. Prenatal DFP, 200 [mu]g/kg, increased weight by PHD 14. DFP did not affect DVs, but increased activity in males at 50 [mu]g/kg and females at 100 [mu]g/kg on PHD 1. DFP increased TI in females, but not males, on PHD 14. DFP decreased pokeweed mitogen-induced and increased lipopolysaccaride-induced lymphocyte proliferation in blood and thymus (respectively) harvested on PHD 16;Experiment 3. Daily DFP (0, 100, or 200 [mu]g/kg) on E 10-12 reduced hatch success, but did not affect weight at hatch or PHD 14. Chicks received 0.0, 0.5, or 1.5 mg/kg scopolamine 30 min before behavioral tests. Prenatal DFP (100 [mu]g/kg) decreased DVs and 1.5 mg/kg scopolamine reversed the effect on PHD 1; there were no activity effects. Scopolamine, 0.5 mg/kg reduced TI except at 200 [mu]g/kg DFP on PHD 14;Experiment 4. Daily DFP (0, 150, or 200 [mu]g/kg) on E 10-12 did not affect hatch success or hatch weight, but increased weight by PHD 14. Chicks received 0.0, 0.25, or 0.5 mg/kg physostigmine 30 min before behavioral tests. On PHD 1, 0.25 physostigmine increased DVs in chicks at 150 [mu]g/kg DFP; activity was not affected. DFP increased TI in females, but not males, and PHY increased TI in females at 0 [mu]g/kg DFP on PHD 18;These data demonstrate perinatal consequences of prenatal DFP that endure into the third week posthatch and are sensitive to cholinergic manipulation.