Human Club Cell Protein (CC16, CC10 and also called uteroglobin, urinary protein 1 or Clara Cell Secretory Protein) belongs to the family of secretoglobins and is a secreted protein product of non-ciliated bronchiolar Club cells. Its function remains to be elucidated but there is convincing data suggesting its phospholipase A2 inhibitory activity as well as a number of other immunomodulatory features including inhibition of interferon gamma signaling and Th1 vs. Th2 lymphocyte regulation. It was proposed as a potential peripheral marker of respiratory epithelial injury and bronchial dysfunction. In serum, its increase is associated with age, asbestos, nitrogen chloride and ozone exposure, sarcoidosis and high PEEP ventilation. Decreased serum CC16 levels are found after pulmonary resection, in silica-exposed workers, smokers and in asthma. Decreased CC16 concentrations were also found in the amniotic fluid of fetuses suffering from pulmonary hypoplasia caused by various mechanisms (diaphragmatic hernia, diabetic fetopathy, Turner and Down syndrome).