The ofloxacin (OFLX) concentration in serum, saliva and pleural effusion was measured in 12 patients with pleural effusion after oral administration at a dose of 200 mg three times a day (600 mg daily). Three patients had non-small cell lung cancer and the others had pulmonary tuberculosis. The mean OFLX levels in the serum, saliva and pleural effusion at 2 hours after the first administration on day 3 was 3.15 +/- 1.52, 3.36 +/- 2.23 and 2.86 +/- 1.77 micrograms/ml respectively. There was a strong correlation among these concentrations. The OFLX concentration of pleural effusion was predictable from that of saliva. A 3-day oral administration is sufficient to achieve the OFLX level of pleural effusion similar to that of the serum. It is possible that OFLX is effective for pleuritis caused not only by common infectious pathogens but also by Mycobacterium tuberculosis.