A study of the effect of prulifloxacin, a new antibacterial agent, during the period of organogenesis was conducted in New Zealand White rabbits. Female rabbits were given prulifloxacin orally at dose levels of 0 (control), 10, 30 and 100 mg/kg from day 6 to 18 of pregnancy. Female rabbits were sacrificed on day 29 of pregnancy for examination of their fetuses. In the 30 mg/kg group, food and water consumption decreased. In the 100 mg/kg group, soft stool was observed and body weight gain, food consumption and water consumption decreased. Premature delivery (2/16) occurred and enlargement of cecum and increased weight of cecum were observed. The number of fetal death increased in the 100 mg/kg group. However, prulifloxacin had no effects on the number of corpora lutea, implantations and live fetuses, and on body weight, placental weight, sex ratio, and external, visceral and skeletal development of live fetuses. These results show that the NOAEL of prulifloxacin are 10 mg/kg for general toxicity in mother animals, 30 mg/kg for pregnancy of mother animals and for development of fetuses.