The aim of the study was to compare the effect of phenobarbital given to pregnant rabbits and of epileptic seizures on the course of pregnancy, the physical state, and central nervous system development of newborns. Phenobarbital was given orally during whole pregnancy or for the last ten days in amounts 18,5 mg/kg/body weight = 0,1 DL 50. Seizures of "grand mal" type were evoked with electrostimulator every day since the tenth day of pregnancy. Phenobarbital penetrates via placenta, reaches the organs of all fetuses, and seizures provoke hypoxaemia of fetuses. Phenobarbital administered during whole pregnancy exerts an teratogenous effect. Both injurious factors applied after teratogenous period cause a retardation of general development of fetuses. After phenobarbital administration slight brain lesions are visible in the light, electron microscopical and histochemical examination. More evident was the retardation of the development of the central nervous system after both of the examined injurious factors. In the brain stem and in the cortex the neurons are less mature and the synaptic junctions in the cortex are less numerous. In our experimental models phenobarbital seems to evoke more noxious effect than seizures in mothers.