We measured the levels of inflammatory cytokines interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-alpha (TNF-alpha) in pleural effusions and serum in 65 consecutive patients: 32 with malignant pleural effusion (MPE) (group A), and 33 with inflammatory benign pleural effusion (BPE) (group B). Serum levels of 15 healthy individuals served as control. Concentrations of IL-1alpha were higher in serum compared to pleural fluid in both groups (47.1+/-33.9 vs. 25.9+/-1.7 fmol/ml, p<0.001, in group A; and 39.9+/-30.9 vs. 25.4+/-16.3 fmol/ml, p<0.02, in group B). Similarly, concentrations of IL-1beta and IL-2 were significantly higher in serum compared to pleural fluid in both groups. In contrast, IL-6, IL-8 and TNF-alpha were found at high concentration in MPE in comparison to serum IL-6: 171.8+/-60.4 vs. 7. 2+/-7 fmol/ml (p<0.001), IL-8: 1175.15+/-2385.6 vs. 285.2+/-187.2 pg/ml (p<0.05), TNF-alpha: 204.9+/-82.9 vs. 79.4+/-31.9 fmol/ml (p<0. 001). Similarly, pleural concentrations of IL-6, IL-8 and TNF-alpha were higher in BPE patients in comparison to serum IL-6: 124.3+/-56. 2 vs. 8.6+/-6.4 fmol/ml (p<0.001) IL-8: 2109.2+/-4121.5 vs. 291. 6+/-197.9 pg/ml (p<0.02), TNF-alpha: 183.8+/-28.2 vs. 86.2+/-23.9 fmol/ml (p<0.001). These data suggest that IL-6, IL-8 and TNF-alpha might be secreted locally at the site of active disease both in benign and malignant pleural effusions.