Cellular and biochemical analyses of bronchoalveolar lavage (BAL) were performed in 8 normal subjects and in 18 patients with pulmonary sarcoidosis. The patients were divided into two groups, according to the intensity of the alveolitis as assessed by lung T-lymphocyte percentage and by 67Ga lung scan. High-intensity alveolitis (HIA) patients had an increased ratio of OKT4-positive: OKT8-positive T cells in their lungs, but not in their blood, compared to low-intensity alveolitis (LIA) patients and to controls. Biochemical analyses of BAL showed that HIA patients had increased albumin and IgG concentrations compared to LIA patients and to controls. IgA concentrations were more elevated in sarcoid patients than in controls, with no difference between the two groups of patients. No differences were detected in IgM concentrations between the three groups of subjects. The levels of different Ig classes were then calculated as a ratio with respect to albumin in order to determine whether their presence in BAL fluid was due to increased alveolar-capillary 'leak'. The IgG:albumin ratio was significantly higher in HIA patients compared to LIA patients and to controls, whereas comparison of the IGA: albumin and IgM: albumin ratios showed no significant differences between the three groups of subjects. These findings suggest that alveolar-capillary permeability is increased in pulmonary sarcoidosis and provide evidence that local IgG production is enhanced in active states of this disease.