Background: Photodynamic bronchoscopy (PDD) allows for early detection of bronchial cancer. Adverse effects and high costs, partly related to general application of photosensitisers, are important limitations of the method. The local application of a photosensitiser could help to minimize these problems. In this study the validity and safety of inhaled 5-ALA have been tested. Methods: We examined 49 patients (age 59±11, cigarette consumption 36±17 pack-years) with present or past respiratory neoplasms and other with increased risk of bronchial cancer by photodynamic bronchoscopy (Storz- D-light) after inhaled 5-ALA. Biopsies were taken from the fluorescence-positive and negative foci (control). Symptoms and pre-/post-inhalation spirometry were analysed. Results: The overall sensitivity was 82%, specificity 62%, positive predicted value (PPV) 45% and negative predictive value (NPV) 90%. Specificity decreased to 53% and PPV to 15% when visible tumours were excluded. PDD, when added to white light bronchoscopy increased sensitivity by 2.1% and NPV by 6%, but decreased specificity by 35.4% and PPV by 53.1%. In a group of actual or past tumours the sensitivity increased by 22% and NPV by 34%, whereas specificity decreased by 26% and PPV by 35%. In 2 cases a drop in FEV1 above 10% of pre-inhalation value was observed but no clinically relevant symptoms were reported. Conclusions: Photodynamic bronchoscopy with inhalation of 5-ALA is a relatively safe diagnostic method. The main disadvantage is high percentage of false positive results. Nevertheless, we believe, that it may be a useful adjunct to conventional diagnostic modes, especially in the detection of early lesions in patients operated due to cancer (stump control and detection of metachronous lesions) and those prepared for operation (synchronous lesions and detection of infiltration margins). However all suspected lesions must be verified by histo-pathological examination.