BACKGROUND: Tuberculous pleural effusion responds well to the anti-tuberculosis agents in general, so no further aggressive therapeutic managements to drain the tuberculous effusion is necessary except in case of diagnostic thoracentesis. But in clinical practice, we often see some patients who later decortication need due to dyspnea caused by pleural thickening despite the completion of anti-tuberculosis therapy in the patients with tuberculous effusion. Especially, the patients with loculated tuberculous effusion might have increased chance of pleural thickening after treatment. The purpose of this study was that intrapleural urokinase instillation could reduce the pleural thickining in the treatment of loculated tuberculous pleural effusion. METHODS: Thirty-seven patients initially diagnosed as having loculated tuberculous pleural effusion were randomly assigned to receive either the combined treatment of urokinase instillation and anti-tuberculosis agents(UK group) and anti-tuberculosis agents(Non-UK group) alone. The 16 patients in UK group received a single radiographically guided pig-tail catheter ranging in size from 10 to 12 French. 100,000 units of urokinase was dissolved in 150 ml of normal saline and instilled into the pleural cavity via pig-tail catheter every day, also this group was treated with anti-tuberculosis agents. While the 21 patients in Non-UK group were teated with anti-tuberculosis agents only except diagnostic thoracentesis. Then we evaluated the residual pleural thickening after treatment for their loculated tuberculous pleural effusion between the two groups. Also the duration of symptoms and the pleural fluid biochemistry like WBC counts, pH, lactic dehydrogenase (LDH), glucose, proteins, and adenosine deaminase (ADA) were compared. RESULTS: 1) The residual pleural thickening (RPT) (5.08 +/- 6.77 mm) of UK group was significantly lower than that (20.32 +/- 26.37 mm) of Non-UK group (P<0.05). 2) The duration of symptoms before anti-tuberculosis drug therapy of patients with RPT >or=10 mm(5.23 +/- 3.89 wks) was significantly longer than the patients with RPT <10 mm(2.63 +/- 1.99 wks) (P<0.05). 3) There were no significant differences in the pleural fluid findings like WBC count, glucose, LDH, proteins, pH, ADA between the patients with RPT >or=10 mm and the patients with RPT <10 mm. CONCLUSION: The treatment of loculated tuberculous pleural effusion with the urokinase instillation via percutaneous transthoraic catheter was effective to reduce the pleural thickening.