To determine whether cytokines are generated in vivo in subjects with asthma, we have measured cytokine levels (tumor necrosis factor [TNF], granulocyte-macrophage-colony-stimulating factor [GM-CSF], interleukin [IL]-1 alpha, IL-1 beta, IL-2, IL-4, and IL-6) in the airways of subjects with symptomatic (N = 24) and asymptomatic (N = 9) asthma with immunoassays (GM-CSF, IL-1 alpha, IL-1 beta, IL-2, and IL-4) or bioassays (TNF and IL-6) and the polymerase chain reaction (IL-1 beta and TNF). Significant levels of TNF (578 +/- 917 pg/ml versus 24 +/- 29 pg/ml) (p = 0.01), GM-CSF (24 +/- 41 pg/ml versus less than 8 pg/ml) (p = 0.02), and IL-6 (225 +/- 327 pg/ml versus 7 +/- 12 pg/ml) (p = 0.01), but not IL-1 alpha or IL-4, were detected in the bronchoalveolar lavage fluid (BALF) of patients with symptomatic compared with BALF of patients with asymptomatic asthma. Levels of IL-1 beta (266 +/- 270 pg/ml versus less than 20 pg/ml) (p = 0.001) and IL-2 (1.4 +/- 2.8 ng/ml versus less than 0.3 ng/ml) (p = 0.05) in BALF in patients with symptomatic compared with that in BALF levels in patients with asymptomatic asthma suggested activation of alveolar macrophages and T cells. Thus, in episodes of asthma, several cytokines, including TNF, GM-CSF, IL-1 beta, IL-2, and IL-6 are detectable in BALF.