We examined the effects of bronchoalveolar lavage (BAL) and BAL fluid characteristics on the systemic proinflammatory cytokine expression and their relation to clinical and laboratory findings. Thirty patients suspected to have lung cancer were subjected to fiber-optic bronchoscopy (FOB) and BAL. Clinical and laboratory findings were determined at baseline, 4 h, and 24 h, including lung auscultation, temperature, chest X-ray, WBC, neutrophils, and serum IL-1beta, IL-6, and TNF-alpha. BAL fluid characteristics were determined including cytokine levels. Fifteen volunteers served as controls to determine serum variation of the same cytokines. Significant temperature elevation was defined as 1 degrees C increase compared to baseline. BAL was associated with temperature and serum TNF-alpha and IL-6 but not IL-1beta increase at 4 h. Four patients (13.3%) developed temperature over 38 degrees C. In controls there were no significant changes between baseline and 24 h measurements for the same cytokines. Eleven patients (36.6%) developed a significant temperature elevation 4 h after BAL. These patients had a statistically significant ( p < 0.05) increase in serum IL-6 at 4 h and in TNF-alpha at both 4 and 24 h after BAL compared with the nonsignificant temperature increase group. BAL characteristics were not different between the two groups. On the other hand, BAL fluid IL-6 and TNF-alpha levels were significantly higher ( p < 0.05) in the nonfever group. Significant temperature increase was observed in 36.6% of the patients undergoing BAL and associated with significant serum TNF-alpha and IL-6 increase at 4 h. Lung cytokines levels, alveolar macrophages, and BAL fluid characteristics are not related to temperature and serum proinflammatory cytokine increase. The hypothesis of alveolar macrophages derive from cytokine production and shift to the systemic circulation cannot be supported by our data.