Using the monoclonal antibodies OKT4 and OKT8, we determined the proportions of helper and suppressor T cells in patients with sarcoidosis and high-intensity alveolitis, patients with sarcoidosis and low-intensity alveolitis, patients with idiopathic pulmonary fibrosis (IPF), and normal controls. In controls and patients with IPF, the ratio of helper to suppressor T cells was 1.8:1 in lungs and blood. In contrast, this ratio was 10.5:1 in lungs (P less than 0.001) and 0.8:1 in blood (P less than 0.05) in patients with sarcoidosis and high-intensity alveolitis. The ratio of helper to suppressor T cells was not higher in the lungs or blood of patients with sarcoidosis and low-intensity alveolitis; on the contrary, because of the higher proportions of suppressor cells, the ratio of helper to suppressor cells was lower in both lungs and blood. In studies of function, lung T cells from patients with sarcoidosis and high-intensity alveolitis released monocyte chemotactic factor (a lymphokine critical to granuloma formation) and polyclonally activated B cells to produce immunoglobulins. We conclude that one determinant of lung injury in sarcoidosis in the presence of large numbers of lung helper T cells, which are important in granuloma formation.