Seven patients have been operated on at St Vincent's Hospital since 1954 in attempts to relieve superior vena caval obstruction. Six of them had carcinoma of the lung, and synthetic bypass grafting was performed in four. The seventh patient had a malignant thymoma excised, with resection of the superior vena cava and replacement by a free pericardial graft. An adenocarcinoma of the lung was also resected at the original procedure. During the twoyear follow‐up he has developed pure red cell agenesis and hypogammaglobulinœm