The detection of the pathogen is of crucial importance for confirming the diagnosis of pneumocystosis. The main material for the study is sputum, bronchial secretions, washings obtained during bronchial lavage or bronchoalveolar lavage, pieces of lung tissue taken during transbronchial, percutaneous or open biopsy. Most often, due to the serious condition of the patient, these manipulations are not carried out in order to avoid complications.