The penetration of ofloxacin into lung tissue was studied in 10 patients subjected to pulmonary surgery. Samples of blood and lung tissue were obtained 3 to 8 h (mean, 5 h) after oral administration of 200 mg. The mean level in tissue was 2.17 ± 0.5 μg/g, while the mean level in serum was 0.85 ±0.23 μg/ml. The mean lung tissue/serum concentration ratio was 2.55 ± 0.30. The achievable levels of ofloxacin in lung tissue are above the MICs for most pulmonary pathogens.