The objective of the study was to determine if residual pleural thickening after treatment for pleural tuberculosis could be predicted from the pleural fluid findings at the time of the initial thoracentesis. Forty-four patients initially diagnosed as having pleural tuberculosis between January 1986 and January 1988 were separated into two groups: the 23 patients in group 1 had residual pleural disease, while the 21 patients in group 2 had no residual pleural disease after treatment for their pleural tuberculosis was completed. The clinical characteristics of the two different groups did not differ significantly, but the patients in group 1 tended to be a little sicker in that the duration of their symptoms was longer, their hemoglobin values were lower, and weight loss and cough were more frequent. There were no significant differences in the pleural fluid findings in the two different groups. The mean pleural fluid protein level was 5.40 +/- 0.58 g/dl for group 1 and 5.17 +/- 0.80 g/dl for group 2, while the mean pleural fluid glucose level was 78.6 +/- 19.5 mg/dl for group 1 and 79.5 +/- 20.1 mg/dl for group 2. The mean pleural fluid lactate dehydrogenase (LDH) level in group 1 was 593 +/- 498 IU/L, while the mean level for group 2 was 491 +/- 198 IU/L. The presence of residual pleural thickening was not related to the chemotherapeutic regimen or the performance of a therapeutic thoracentesis. From this study we conclude that approximately 50 percent of patients with pleural tuberculosis will have residual pleural thickening when their therapy is completed, but that one cannot predict which patients will have residual pleural thickening from either their clinical characteristics or their pleural fluid findings.