Treatment of 28 patients with malignant pericardial effusion was accomplished primarily by intrapericardial instillation of radioactive chromic phosphate. At time of diagnosis of pericardial disease, 14 patients had major manifestations of tamponade; the rest had little or no clinical evidence of effusion. Only eight of the 28 patients had further problems with effusion after the initial pericardiocentesis and 32P instillation. Additional aspirations were done on those patients 2 weeks to 5 months later. The average survival was 9 months; seven patients lived more than 1 year.