Peripheral reticulocyte micronucleus assays using acridine orange supravital staining were performed on mice (ddY), rats (SD), rabbits (JW), dogs (beagle), and monkeys (crab-eating), with cytosine arabinoside (ara-C) as the model chemical. Animals received a single intraperitoneal (mice and rats) or intravenous (rabbits, dogs, and monkeys) injection of ara-C at dose levels of 12.5 (except monkeys), 25, and 50 mg/kg body weight. 5 μl samples of blood were collected immediately before the treatment and 12, 24, 30, 36, 48, 54, and 72 h after treatment in mice, rats, and rabbits, and 24, 48, and 72 h for dogs and monkeys. We analyzed 1000 reticulocytes per animal.Micronucleated reticulocytes (MNRETs) were induced in all species, with the highest frequency in mice. MNRET frequencies in rabbits, dogs, and monkeys were approximately half of that in mice, and in rats it was only one fifth of that of mice. The post-treatment MNRET frequencies peaked at 30 h in mice and rats, 36 h in rabbits and dogs, and 72 h in monkeys. It may be considered that these results are due to the differences in metabolism of ara-C and in removing MNRETs by the reticulo-endothelial system in the spleen.In the present study, the peripheral reticulocyte micronucleus assay was applicable in other mammalian species such as mice. Therefore, it was suggested that the peripheral reticulocyte micronucleus assay could be done with other ongoing toxicological studies.