The mechanisms of sarcoidosis (Besniera-Boeck-Schaumann disease, BBS) remain incompletely understood, although recent observations suggested an important contribution of interleukin-33 (IL-33). So far, there are no data about bronchoalveolar lavage fluid (BALF) concentration of IL-33 in patients with BBS. In the present study we attempted to relate the concentration of IL-33 to IL-18, a well-known marker of BBS activity, in BALF of BBS patients. We examined 24 BBS patients (stage II). The age-matched control group consisted of 24 healthy subjects. The levels of IL-33 and IL-18 in BALF were higher in BBS patients than in the control group [IL-33: 4.8 (0.1-12.5) vs. 3.4 (0.6-56.9) pg/ml, p=0.024; IL-18: 33.2 (5.7-122.0) vs. 10.8 (1.9-45.8) pg/ml, p=0.002]. In the BBS group, the correlations between IL-33 and IL-18 (r=0.606, p=0.002), and between IL-33 and diffusion lung capacity for carbon monoxide (DLCO) (r=-0.500, p=0.035) were found. The receiver-operating characteristic curves were applied to find the cut-off serum levels of IL-33 and IL-18 in BALF (BBS vs. healthy: IL-33 2.7 pg/ml and IL-18 16.4 pg/ml). We conclude that IL-33 appears an important factor of pulmonary BBS activity.