[en] To investigate the clinical course and the prognosis of carcinomatous pleuritis following local therapy, we studied 101 CT films of 53 cases of carcinomatous pleuritis complicated with primary lung cancer. The histological types of the 53 cases included 43 adenocarcinomas, 4 squamous cell carcinomas, 4 small cell carcinomas and 2 large cell carcinomas. The median survival time was 6 months after the initial i.p. instillation. The mean number of i.p. instillations was 6.1 times, median was 3. Instillated drugs were adriamycin, OK-432, ACNU, Mitomycin, aclacionorubicin or others. The loculated pleural space was observed in 21 cases (39.6 %), and the loculation of 13 cases developed within 1 month after the initiation of the local therapy or with less than 3 times i.p. instillation. In 12 out of 13 cases, malignant cells remained or reappeared in pleural effusion in spite of local treatment after the loculation. There was no statistical significance between the mean survival time of cases with loculated pleural space (4 months) and that of cases without loculation (8 months). The i.p. instillation of sclerosing agents are accepted to be rational and useful in the treatment of malignant pleural effusion. On the other hand, the drug instillation seems to have the disadvantage of the development of the loculated pleural space in the early stage of the local therapy. The loculation of the pleural space not only made it difficult to remove the pleural effusion and to reexpand the lung, but also was one of the causes of refractry pleuritis. So, to minimize the development of loculation, it is suggested that local therapy should be begun as soon as possible after the detection of the pleural effusion with the aim of complete reinflation of the atelectatic lung and complete closure of the pleural space (pleurodesis). (J.P.N.)