Idiopathic pulmonary fibrosis is the most common of the idiopathic interstitial lung diseases referring to the histo-pathological entity of usual interstitial pneumonia. It has been hypothesized that inflammation may trigger the multiformic fibrotic lesions found in the affected lung, and defects in the innate immune defense, including the complement, can predispose to pulmonary fibrosis. The polymorphism C5507G in the Complement Receptor 1 gene has been recently associated with idiopathic pulmonary fibrosis. C5507G causes an amino acid change from proline to arginine, and opens a potential cleavage site for trypsin-like enzymes and, therefore, a potential mechanism for increased shedding of the molecule from the cell surface. We studied the polymorphism in 96 Finnish patients with idiopathic pulmonary fibrosis and 164 population based controls. All the patients and controls were C5507 homozygous suggesting that either the Finns do not carry the G5507 polymorphism or it is extremely rare. We conclude that G5507 is not a susceptibility allele for idiopathic pulmonary fibrosis among Finnish patients.