Peri- and post-natal effect of HAPA-B, a new aminoglycoside antibiotic, was studied in Jcl: Wistar rats. The antibiotic was given intramuscularly to dams at doses of 25, 100 and 200 mg/kg from day 17 of gestation to 21 days after delivery and throughout lactation. Influences of the drug on dams and their offspring were studied. A decrease in food intake and an increase in water intake were observed in the 200 mg/kg treated group. At autopsy of dams after weaning, pale discoloration and hypertrophy of the kidney were observed in 100 and 200 mg/kg groups. All other observations including delivery and nursing performance of dams, postnatal development of offspring, behavior and reproduction performance of the offspring were normal. The no effect dose level of HAPA-B found in this study was 25 mg/kg on rat dams and 100 mg/kg on the offspring.