Primary ciliary dyskinesia (PCD) is a rare disease, caused by impairment of the motile cilia. Patients present with chronic upper and lower respiratory tract infections. The therapy is mainly supportive and based on that of cystic fibrosis. Chest physiotherapy is one of the cornerstones of the therapy, however the influence of chest physiotherapy on lung function (short term and long term) is not clear. For interpretation of longitudinal lung function data it is important to examine the short time effect of chest physiotherapy. We hypothesize that a session of chest physiotherapy improves lung function and that thus lung function tests must be performed in a standardized way.