Cystic fibrosis (CF) is a model of chronic disease that received in last several years worldwide attention of numerous scientists. The identification of the CFTR gene enabled more detailed investigations of CF pathogenesis and opened the possibility of novel therapeutic approaches. In addition, hopes of casual treatment became more realistic. By providing early diagnosis, combined with modern treatment schemes, CF patients may remain in optimal status and thus potentially profit from the upcoming fundamental changes in CF therapy. The basis of diagnosis remains clinical suspicion. It is based on the presence of characteristic respiratory and/or gastrointestinal symptoms, on the occurrence of CF in the family and/or on positive screening results. Recently, we are diagnosing an increasing number of atypical or monosymptomatic forms of CF such as: chronic „idiopathic“ pancreatitis, chronic sinusitis or obstructive azoospermia. Currently, it is possible to diagnose CF solely on the basis of positive family history and/or based on a positive screening test. The diagnosis of CF is confirmed by laboratory detection of two disease-causing CFTR mutations, observation of increased sweat chloride concentra- tions (> 60 mM) and/or changes in transepithelial nasal potential differences (NPDs). Although, the sweat test remains as a basis of CF diagnosis, border-line or even negative sweat chloride concentrations do not rule out the diagnosis of CF in a patient with positive clinical findings and/or with two CFTR mutations in his/her CFTR gene. Similarly, we cannot exclude the diagnosis of CF in a patient where we did not detect any CFTR mutation, but who has high sweat chloride concentrations. Auxillary laboratory examinations, that may help to establish the diagnosis of CF in suspicious or controversial cases, include: pancreatic function tests, evidence of Pseudomonas aeruginosa infection or presence of another microorganism typical for CF, typical X-ray features, lung obstruction detected by pulmonary function tests (PFTs) and finally the presence of azoospermia in males.

        Key words: cystic fibrosis, sweat tests, molecular-genetic diagnosis, CFTR gene