Hypersensitivity Pneumonitis (HP) is an immunologically mediated interstitial lung disease that may result from repeated inhalation of many different environmental agents. Heterogeneity of the clinical presentation and bronchoalveolar lavage profiles have been described, possibly related to different occupational exposures. The aim of our study was to compare bronchoalveolar lavage fluid (BALF), clinical, functional and radiological characteristics of the two most frequent forms of HP seen in our practice: Suberosis (an HP related to moldy cork dust exposure) and bird fancier's disease (BFD). We included 81 patients with Suberosis, with a mean age of 38.8 +/- 11.3 years and a mean exposure of 20.0 +/- 10.5 years and 32 patients with BFD, with a mean age of 46.3 +/- 11.8 years and mean exposure of 10.5 +/- 1.0 years. Patients with BFD had more acute forms, while subacute and chronic presentations predominated in Suberosis. Restrictive defect was the most frequent pattern of lung function impairment, and more severe in BFD. Ground glass opacities were the most frequent pattern in high-resolution computed tomography. A normal chest x-ray was more frequently seen in Suberosis. Both types of HP had lymphocytic alveolitis in BALF: Suberosis - 6.6 +/- 5.7 x 10(5) ml-l cells, 58.8 +/- 18.9% lymphocytes; bird fancier's disease - 9.0 +/- 6.5 x 105 ml-l cells, 61.7 +/- 22.2% lymphocytes. Although BALF CD8+ lymphocytes predominated in both diseases, the proportion of CD4+ and CD4/CD8 ratios were significantly higher in bird fancier's disease (Suberosis: 0.47 +/- 0.33 versus BFD: 1.1 +/- 1.5; p < 0.005). Moreover, BALF cellularity and mast cell counts were also significantly higher in BFD. In conclusion, Suberosis and bird fancier's disease are HP with different clinical and laboratory profiles, suggesting that despite their pathophysiological similarities, different antigenic exposures may cause different immune and inflammatory response dynamics in the lung.