A family containing 12 subjects spanning three generations and including six cases with clinical evidence of definite or probable fibrosing alveolitis has been investigated. Histologic confirmation was available for three cases. The subjects were between 15 and 54 years of age at diagnosis. Although the size of the sample is small, the mode of inheritance of fibrosing alveolitis within this family appeared to be dominant with incomplete penetrance. HLA typing showed that at least one of the affected siblings did not share any HLA haplotypes with other affected siblings in the third generation. This makes it unlikely that a disease gene would be in association with HLA genes on chromosome 6. In contrast, all affected siblings, as well as two as yet unaffected siblings, carried the immunoglobulin haplotype Gm 1. These studies indicate that familial fibrosing alveolitis in this family may be inherited by a dominantly inherited gene located on chromosome 14 close to the loci encoding for Gm.