Three patients with cardiac tamponade caused by malignancy were treated by pericardiocentesis with intrapericardial OK-432 instillation. The underlying disease was adenocarcinoma of unknown origin, breast cancer and multiple myeloma. Under electrocardiographic monitoring, a polyethylene catheter with several side holes was inserted into the pericardial sac, and after a maximal volume of fluid was withdrawn, 5 KE of OK-432 diluted in 20 ml of saline was instilled through the catheter. All the patients who received intrapericardial OK-432 therapy obtained complete control of pericardial effusion for more than 30 days. The side effects were fever, chills and chest pain which were easily controlled by antipyretics.