From a retrospective study of 80 cases of heart transplantation, the contribution of chest X-rays to the diagnosis of viral pneumonia was studied. Among 66 episodes of pneumonia, a viral cause was proved in 16 cases (CMV: 9, Herpes: 7), with 13 cases during the first 4 months. CMV pneumonia was revealed in 3 cases by a diffuse pulmonary infiltrate with a rapidity fatal outcome and in 6 cases by focal infiltrates that disappeared within 1 and 7 weeks. Herpes pneumonia was immediately revealed, in 5 cases, by a diffuse infiltrate. In 11 out of 16 cases, the viral pneumonia improved but its course was complicated by the development of another pneumonia.