Serum laminin P1 was studied in patients with small cell lung cancer (SCLC), non-small cell lung cancer (NSCLC), respiratory infections, pulmonary fibrosis, and in normal subjects. The level of serum laminin P1 was elevated (greater than 1.27 U ml-1) in 58.9% of SCLC and in 11.5% of NSCLC patients. Median value in SCLC was significantly higher than that in NSCLC (P less than 0.01), respiratory infection (P less than 0.01), and in normal subjects (P less than 0.01), but not statistically different from that in pulmonary fibrosis. The levels of serum laminin P1 in SCLC were related to therapeutic response. However, no certain correlation was established between the level of laminin P1 and the clinical stage of SCLC.