The pharmacokinetics and tissue distribution of DA-3285 (recombinant human erythropoietin, recently manufactured by Research Laboratories of Dong-A Pharmaceutical Company) were studied in the laboratory animals. The plasma, urine, and tissue concentration of DA-3285 were measured by a double-antibody sandwich enzyme immunoassay. After intravenous administration of DA-3285, 20, 100, 500 and 2500 units/kg to rats, the plasma concentrations declined polyexponentially with the terminal half-lives of 2.15, 2.10, 2.31, and 2.35 hr, respectively. Total body clearance (20.7∼26.6 mι/hr/kg) and apparent volume of distribution at steady state (57.2∼70.1 mι/kg) were independent of the dose and AUC increased proportionally with the dose. The renal clearance was much lower than total body clearance, suggesting that extrarenal clearance, presumably metabolism , plays a significant role in elimination of DA-3285. In all rat tissues, the tissue to plasma ratios were smaller than unity, indicating less affinity of DA-3285 to rat tissues and was proved by considerably less value of Vdss. After 3 times a week for consecutive 3 weeks i.v. administration of DA-3285, 100 units/kg to rats, the plasma concentrations and pharmacokinetic parameters of DA-3285 were not significantly different from those in a single administration. After s.c. administration to the rat, plasma concentrations of DA-3285 peaked at 6 hr and the extent of bioavailability was 26.7%. In mice, rabbits and dogs, at DA-3285 dose of 100 units/kg, the mean terminal haw-lives were 2.78, 3.05, and 4.01 hr, respectively. Compared with reported data in the literatures, DA-3285 has similar properties to rh-EPO manufactured by other companies in view of pharmacokinetics.