T lymphocytes and alveolar macrophages accumulating in the lower respiratory tract of patients with pulmonary sarcoidosis are known to be activated to produce several cytokines, presumably leading to granuloma formation within the lung. We hypothesized that these cells produce colony-stimulating factors (CSFs), which have been shown to affect the proliferation and function of monocyte-/macrophage-lineage cells. To test this hypothesis, we tried to detect mRNA encoding CSFs in cells obtained by bronchoalveolar lavage using a reverse transcription-polymerase chain reaction. Granulocyte-macrophage CSF (GM-CSF) mRNA was detected in five of six patients with pulmonary sarcoidosis, whereas it was detected in none of the five normal controls. Macrophage-CSF mRNA was detected in all subjects examined, and interleukin-3 mRNA in none. These results suggest some relation of GM-CSF to sarcoid lesion formation.