The pharmacokinetics of levofloxacin was evaluated in Toxoplasma gondii infected and control mice. Single dose of levofloxacin (10 mg/kg b.w.) was administered orally to the T. gondii infected and control mice. The experimental infection was done by intraperitoneal administration of 200 W of antigen solution (antigen solution concentrations were prepared under microscope at x40: 5, 10, and 20 trophozoites per microscopic field) per mouse from each concentration. Plasma concentrations of levofloxacin were determined by high performance liquid chromatography. Following the administration of levofloxacin, T. gondii infection resulted in significant reduction (p<0.05) of the distribution half life (t(1/2 alpha)) parameters and also in increase of the peak drug concentration (C-max) compared with in control group. Also the area under curve (AUC) and mean resistance time (MRT) values of levonoxacin in T. gondii infected group (4.72 +/- 1.03 and 6.63 +/- 0.71, respectively) were found smaller than in control group (6.12 +/- 0.72 and 8.46 +/- 0.27, respectively). The study results show that a clinician may have to suitably modify the dosage regimens of the levofloxacin while setting up therapy of bacterial infection or other disease.