Behavioral teratogenicity of chlorpromazine (CPZ) was studied in rats by observing the spontaneous motor activity level and learning behavior of light-dark discrimination in the second generation. The dams were treated with CPZ from day 17 of gestation to postpartum day 21 at doses of 2 mg/kg sc. once daily in one group and 4 mg/kg sc. twice daily in the other. The activity level of F1 was measured at 6 to 7 weeks of age for 68 hrs by a magnetic field counter. The learning experiments were started at 5 weeks of age in one group and 15 weeks of age in the other on the behaviors of the continuous food reinforcement at the beginning, then the light-dark discrimination, and finally the reversal discrimination learning. As the results, no influence of the CPZ treatment was observed in the activity level and learning behaviors of the continuous food reinforcement and light-dark discrimination. But, in the reversal learning of the light-dark discrimination an impairment or delay was observed in some F1 of the CPZ groups. Thus, the significance of observing reversal learning behavior in the assessment of the behavioral teratogenicity of drugs has been shown.