SFTPB and cystic fibrosis: The major physiologic form of pro-SP-B with a molecular weight of 24–25 kDa was found in the lavages of all 21 patients with CF, 14 of 15 children with chronic bronchitis, 12 of 14 patients with pneumonia and 13 of 14 children and young adults from the control group (overall in 94%) (Fig. 1A).