The HSV (1 or 2) is the cause of serious pulmonary infections among patients who have had a transplantation. This study in retrospect is based on the analysis of 145 patients who underwent a cardiothoracic transplant at the CHU. in Nancy. Confronted with clinical signs calling to mind breathing difficulties, the analysis of the broncho alveolar lavage (or of the bronchial brushing) revealed the viral aetiological agent. The answer from the laboratory is quickly available by immunofluorescence or by immunoperoxidase with viral anti-protein monoclonal antibodies and by the multiplication in vitro of the virus into cell cultures. The HSV 1 was responsible for 8 herpetic lung infections. The specific Acyclovir treatment was used 6 times successfully. When such a direction of treatment was impossible (in 2 cases) the outcome was fatal. The carry HSV is highly frequent and recurrences under immuno-suppressor treatment require an Acyclovir prophylaxis among patients admittedly carrying the virus in a pre-transplanted serum assessment.