The authors describe their initial experience with the use of high resolution computed tomography (HRCT) in diffuse lung diseases. They analyze in detail the examination technique, different parameters of the visualization modus, aiming of the scan and the standard procedure in HRCT examinations. They demonstrate also the picture of normal anatomical structures on HRCT pictures and morphological types of changes reflecting pathological processes in the pulmonary parenchyma. In a group of 21 patients the most frequent disease was idiopathic pulmonary fibrosis or suspected fibrosis, suspected carcinomatous lymphopathy, pulmonary emphysema incl. the vanishing lung syndrome, exogenous allergic alveolitis and alveolar microlithiasis, diffuse pulmonary affections in collagenoses and Crohn's disease. When the clinical findings are considered concurrently, the HRCT picture is fairly pathognomic and contributes to the establishment of the final diagnosis. In idiopathic pulmonary fibrosis CT and HRCT give a more accurate idea of the extent, grade and frequently also stage of the disease, and as compared with a simple X-ray of the chest, it is a more accurate and more sensitive method. It may be assumed that gradually it will become a standard examination method in diffuse pulmonary diseases.