A study of the effect of prulifloxacin, a new antibacterial agent, during the period of organogenesis was conducted in Sprague-Dawley rats. Female rats were given prulifloxacin orally at dose levels of 0 (control), 30, 300, and 3000 mg/kg from day 7 to day 17 of pregnancy. Twenty-four or twenty-five female rats per dose level were sacrificed on day 20 of pregnancy for examination of their fetuses, and the pregnant rats (12-15 per dose levels) were allowed to deliver naturally for postnatal examination of their offspring. In the 300 or 3000 mg/kg groups, the food consumption decreased and water consumption increased in the dams. In the 3000 mg/kg group, the body weight gain was suppressed in the dams. In the 300 and 3000 mg/kg groups, the weights of cecum increased and the enlargement of cecum was observed. In the 3000 mg/kg group, white spots and rough surface of the kidney and renal tubular nephrosis with crystalline substance were observed and the weight of the kidney increased in the dams, and the body weight decreased and retarded ossifications in the fetuses. Prulifloxacin had no effect on the number of corpora lutea and implantations, or on fetal mortality, sex ratio, or external and visceral development of the fetuses. Prulifloxacin also did not affect delivery and the number of live newborns and birth index, or have any adverse effects on the postnatal development of the first generation offspring (F1) such as differentiation, functional development, emotionality, motor ability, learning ability or reproductive performance. Prulifloxacin also had no adverse effects of the second generation offspring (F2). These results show that the NOAEL of prulifloxacin are 30 mg/kg for general toxicity in mother animals, 3000 mg/kg for pregnancy and delivery of mother animals and 300 mg/kg for development of their offspring.