Our study investigated the presence of IL-8 in pleural exudates from tuberculosis patients (TBP) (n = 13), and evaluated whether it was related with the profile of major immunocompetent cells present in their pleural and peripheral compartments. To allow comparisons, an additional group of patients with parapneumonic pleural effusions (PNE) (n = 7) was included. Blood peripheral immunophenotypic studies were also carried out in 12 age-matched healthy controls (Co), and 39 tuberculosis patients classified, according to the extent of pulmonary involvement, into mild (n = 9), and advanced (n = 30) cases. Patients were recruited before starting therapy, had HIV negative serology, and showed no age differences among groups (mean +/- SD., 40.7 +/- 14.7 years). IL-8 concentrations were measured by an ELISA method while immunophenotypic analysis was performed by using FITC-conjugated monoclonal antibodies reacting against the following cell surface molecules: CD3, CD4, CD8, CD25 (IL-2R+ cells), CD19, and CD68. IL-8 was detected in all pleural exudates though levels in the TB patients, 384 +/- 110 pg/ml, appeared significantly higher than the PNE group, 185 +/- 110 pg/mg, (P < 0.015, mean +/- S.D.). In turn, the former group presented values of pleural CD3+, CD4+, and CD25, which were found increased in comparison with PNE patients (P < 0.01). Unlike the pleural compartment, patients with TBP showed a marked and significant decrease in their circulating levels of cells bearing the CD3, CD4, CD19, CD25, and CD68 phenotypes not only when comparing with Co but also with PNE and mild patients. Differences between the levels of pleural and peripheral T-cells from TBP patients may be the reflection of an important influx of T-lymphocytes from the circulatory system to the pleural cavity, probably linked to the presence of chemotactic factors within the pleural fluid like IL-8.