Lung microdialysis has been used with rats to investigate antibiotic distribution after single-dose administration. However, conducting such experiments after intravenous infusion at steady state would constitute a more convenient alternative, which was evaluated here, using levofloxacin (LVX) as a test compound. Microdialysis probes were inserted in blood and muscle, used as a comparator, between 9:00 a.m. and 11:00 a.m. Intravenous LVX infusion was started 6 h later and maintained until the end of the experiment at a rate of 1.0 mg.h(-1). Lung microdialysis probes were inserted on the morning of the next day. Rats were kept anesthetized during dialysate collection. In vivo probe recoveries were estimated by retrodialysis using a calibrator method, with ciprofloxacin (CIP) as the calibrator. LVX and CIP were analyzed in dialysates by high-performance liquid chromatography. The steady-state tissue-to-blood unbound-drug concentration ratios were 1.00 +/- 0.15 in muscle tissues and 1.06 +/- 0.40 in lungs, suggesting passive distribution of LVX in tissue. Although providing no information on rate of distribution, microdialysis investigations following drug infusion at steady state appear to be an interesting approach for characterization of antibiotic distribution in rat lungs.