146 of 226 patients suffering from Hodgkin's disease were submitted to a high voltage therapy in the chest using the method of single fields. In order to be in a position to judge the appearance and the development of a modification of the pulmonary parenchyma induced by radiations, the authors evaluated the data of 69 patients who could be checked up in relatively small intervals during at least one year after the radiotherapy. Dilatations of interpleural and hilar lymphomas or pulmonary infiltrates have to be considered as one of the most important causes of atypical pneumonia and fibrosis induced by radiation. 12 patients out of 35 (i.e. 35,3%) with intrathoracic lymphomatosis granulomatosa presented atypical pneumonias which mostly were not very serious, and four patients (i.e. 11,8%) had fibroses. If the mediastine was irradiated systematically for the purpose of prophylaxis, no pulmonary reaction was observed that could be demonstrated by means of X-rays.