To determine if MUC-031 cleaves the major gel forming mucins in the airway (MUC5B and MUC5AC), we compared the effects of rhDNase and increasing concentrations (0.1–10 mM) of MUC-031 and dithiothreitol on the size of MUC5B and MUC5AC in Western blots of CF sputum. Here, MUC5AC is linked to cystic fibrosis.