Hyaluronate is a potential marker of activated pulmonary fibroblasts and appears in increased amounts in bronchoalveolar lavage fluid from patients with sarcoidosis. This study was performed to investigate a possible link between the local immune response and pulmonary fibroblast proliferation. The median hyaluronate concentration in the lavage fluid from 23 sarcoid patients was 12.0 (interquartile range 7.5-28.5) micrograms/l. The hyaluronate concentration was positively correlated to the concentration and proportion of lymphocytes (p less than 0.001 and p less than 0.01, respectively) as well as to the concentrations of T lymphocyte subsets (OKT4+ p less than 0.01, OKT8+ p less than 0.05). No correlation was found between the hyaluronate concentration and the OKT4+/OKT8+ ratio. Furthermore, a significant correlation was observed in the lavage fluid between hyaluronate and angiotensin-converting enzyme, a marker of monocyte/macrophage activity (p less than 0.01). Thus, the intensity of the sarcoid alveolitis was associated with biochemical signs of pulmonary fibroblast proliferation/activation in sarcoidosis.