The pharmacokinetics and urinary excretion following single intramuscular administration of levofloxacin at a dose of 4 mg/kg was investigated in seven male cross bred calves. Appreciable plasma concentration of levofloxacin (0.38 ¡¾ 0.06 ¥ìg/ml) was detected at 1 min after injection and the peak plasma level of 3.07 ¡¾ 0.08 ¥ìg/ml was observed at 1 h. The drug level above MIC₉₀ in plasma was detected up to 12 h after administration. Rapid absorption of the drug was also evident by the high value of the absorption rate constant (2.14 ¡¾ 0.24 /h). The overall systemic bioavailability of levofloxacin, after intramuscular administration, was 56.6 ¡¾ 12.4%. The high value of AUC (7.66 ¡¾ 0.72 mg . h/ml) reflected the vast area of body covered by drug concentration. Extensive distribution of the drug into various body fluids and tissues was noted by the high value of Vd_area (1.02 ¡¾ 0.05 l/kg). The high ratio of AUC/MIC (76.6 ¡¾ 7.25) obtained in this study indicated excellent clinical and bacteriological efficacy of levofloxacin in calves. The elimination half-life and MRT were 3.67 ¡¾ 0.4 h and 5.57 ¡¾ 0.51 h, respectively. The total body clearance (Cl_B) was 204.9 ¡¾ 22.6 ml/kg/h. On the basis of the pharmacokinetic parameters, a suitable intramuscular dosage regimen for levofloxacin in calves would be 1.5 mg/ kg repeated at 12 h intervals.