To determine the efficacy of OK-432 as pleural sclerosant, we examined the outcomes in 81 patients (age : 27 to 82 years) with malignant pleural effusion and the outcomes in 64 patients ecieving OK-432 3-10KE(1 Klinische Einheit unit) through a chest tube for malignant pleural effusions. Of 81 patients with malignant pleural effusion, 40 patients had lung cancer. Lung cancer is the most frequent cause of malignant pleural effusion in men and women, in which 57 oyo of it was adenocarcinoma. Eighty seven percent of patient had respiratory symptom. Of the 64 patients with intracavitary injection of OK-432 for malignant pleural effusion, 59 patients had a complete short-term response (no fluid reaccumulation during 1 month after intracavitary injection of OK-432). Five patiens of the non-responders had partial control of effusion, with improvement in respiratory symptoms and these patients underwent thoracentesis. Of the 51 patients who survived longer than 1 month, 48 patients did not have re- accumulation of the fluid during follow up. Fever after intracavitary injection of OK-432 was a majors side effect although but that was easily controlled with non-steroidal anti inflammatory drug therapy, Thus the efficacy of intracavitary OK-4)2 injection for malignant pleural effusion was very helpful.