Based on previous publications, the distribution of CCSP expression in non-ciliated Clara cells is described as cytoplasmic [23, 24, 25] . We made the surprising and novel discovery of CCSP immunoreactivity along cellular membranes of bronchiolar Clara cells. Using pan-cadherin as a cell membrane marker in normal airway epithelium [18, 26, 27] we found CCSP was expressed not only in the cytoplasm, but also in the membrane. These findings gave rise to the possibility that living Clara cells can be isolated by flow cytometry using fluorescing tags. Our successful CCSP + cell sorting further confirmed the distribution of CCSP membranous expression. One explanation is that bronchiolar Clara cells secrete such large quantities of CCSP that part of it remains stuck to the outer surfaces of cell membranes, allowing sorting of CCSPcontaining cells from suspension. Clara cell isolation from rabbit was first reported in the early 1980s by Devereux et al. [28] . After that, several groups were able to isolate pulmonary Clara cells from mouse [29, 30, 31, 32, 33] . The studies have been instrumental in establishing the many functions of Clara cells. However, the majority of the methods are quite complex and rely on protease digestion followed by centrifugal elutriation and/or Percoll density gradient centrifugation. Only one group used FACS for Clara cell isolation from rat based on the reaction of their glutathione content with monochlorobimine to a fluorescent product [34] . The techniques typically resulted in a Clara cell enrichment of 55,90%. A reproducible source of considerably purified Clara cells is necessary for airway stem/ progenitor cell research. Using high concentrations of collagenase for lung tissue digestion followed by flow cytometry sorting, we were able to achieve 98% pure CCSP + (Clara) cell population, providing a very useful and reliable method for Clara cell function and stem cell research. A notable application will be to directly address molecular mechanisms of genes that have been expressed in Clara cells by using CCSP as a lung specific promoter in transgenic mice.