Background: Hypersecretion of mucus plays an important role in the pathogenesis and severity of asthma. The primary proteins in mucus are mucin glycoproteins; MUC-5AC is the primary airway mucin gene. The calcium chloride-activated channel gene hCLCA1 (gob-5 in the mouse) has been suggested to increase MUC-5AC gene expression, and both are increased in asthmatic patients and murine models. TNF-α increases the expression of these genes in vitro but has not been investigated in vivo. Objective: We sought to determine whether TNF-α increases gene expression of gob-5 and MUC-5AC and induces mucus cell metaplasia in vivo. Methods: Naive BALB/c mice received 50 ng of recombinant murine TNF-α (rmTNF-α) intratracheally daily for 1, 2, or 3 weeks; another group received the same dose of intratracheal rmTNF-α daily for 3 weeks and then alternate-day treatment for 3 additional weeks (total of 6 weeks). AKR mice received 50 ng of rmTNF-α intratracheally for 3 or 6 weeks daily. Naive nontreated mice were used as control animals. Airway gene products for gob-5 and MUC-5AC were determined by means of real-time PCR. Lung tissue sections were stained with periodic acid-Schiff/Alcian blue to assess mucus cell metaplasia. Results: rmTNF-α significantly increased gene expression of airway gob-5 and MUC-5AC after 2 weeks in the BALB/c mice. There was noticeable mucus staining in all mice treated for at least 3 weeks with TNF-α and in 80% of the mice receiving 2 weeks of treatment. After 3 weeks of treatment, the AKR mice also showed increased gob-5 expression. Conclusions: This study demonstrates for the first time that TNF-α alone in vivo is sufficient to increase airway mucus gene expression in 2 murine strains.