1. The pharmacokinetics and bioavailability of enrofloxacin in chickens were investigated following intravenous, intramuscular, subcutaneous and oral administration of 10 mg/kg body weight. A rapid distribution phase was followed by a slower elimination phase. 2. The apparent volume of distribution was 2.2 l/kg. Absorption half lives were 0.37, 0.36 and 0.92 h; elimination half lives were 4.06, 4.48 and 4.29 h and bioavailabilities were 87.5%, 80.8% and 59.6% after intramuscular, subcutaneous and oral administration, respectively. The drug completely disappeared from all tissues after 3 days following oral administration. 3. Based on the bioavailability and disposition kinetics of enrofloxacin, administration of one dose per day should both be practical and adequate to maintain plasma enrofloxacin concentrations within the pharmacologically active but lower than tolerance limit.