Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease of unknown etiology, with an appearance of usual interstitial pneumonia on lung biopsy. To-date, about a 100 families diagnosed with IPF have been described. Familial IPF is defined as histologically confirmed IPF occurring in two or more members of a family. Familial pulmonary fibrosis is hereditary, most probably as a feature which is autosomal dominant with variable penetration. Since 2002, we have been following two families with IPF, referred to in the present article as A and B. The patients in Family A included brother, sister, and sister's daughter. We examined two closest relatives of the patients in family A who are healthy. The patients in Family B included father and his two children. In Family B, we examined six other closest relatives, all of whom proved healthy. In all cases, IPF diagnosis was confirmed histologically. We examined human leukocyte antigen (HLA) alleles in both families, including antigens Class I (locus A, B, and C) and Class II (locus DR). On the basis of the results obtained it is impossible to determine the relation between major histocompatibility complex (MHC) polymorphisms and the incidence of the disease.