Forty-one cases of adenocarcinoma of the lung with pleuritis carcinomatosa were randomly assigned to either chemotherapy alone or chemoimmunotherapy using Nocardia rubra cell wall skeleton as immunopotentiator. In 34 evaluable patients, the rates of volume decrease and the disappearance of tumor cells in pleural effusion were higher in chemoimmunotherapy group than in chemotherapy alone group, and median survival times from the beginning of treatment in chemotherapy alone and chemoimmunotherapy groups were 189 and 266 days, respectively. The survival times in patients with stage III and P.S. 0+1+2 were better than those in patients with stage IV and P.S. 3, respectively. Transient fever and mild elevation of GPT and GOT were tolerated without any treatment.