Laminin is a noncollagenous component of the extracellular matrix in the alveolar wall and may play a role in the development of fibrotic lung disease. Serum levels of laminin fragment P1 as well as procollagen III peptide were determined in 28 patients with pulmonary sarcoidosis and 10 healthy controls using specific radioimmunoassays. The patients' results were compared with the clinical appearance, lung function values (vital capacity, total lung capacity, FEV1, transfer coefficient (KCO), and alveolar-arterial oxygen difference during exercise) and serum concentrations of angiotensin converting enzyme and soluble interleukin 2 receptor. Laminin levels in patients were significantly higher than in controls but always remained within normal limits. Although there was a tendency towards higher values in patients with active disease and with radiographic involvement, no significant correlation was found between laminin concentration and clinical, functional or biochemical data. In contrast, procollagen III N-terminal peptide concentrations were elevated in 19 of 28 patients and showed a weak but significant inverse correlation with parameters of restriction with significantly higher values in patients with active disease. In conclusion, serum levels of laminin fragment P1 are not elevated in pulmonary sarcoidosis and do not correlate with other parameters of the disease. Yet serum levels of procollagen III N-terminal peptide were associated with the degree of parenchymal involvement as expressed by functional disturbance and with active disease.