From 1970 to 1976, 268 patients with pleural effusions underwent local therapy with the polyenzyme preparation Wobemugos; 235 patients were evaluable regarding the effectiveness of this therapy. In 115 of the cases, the primary tumour was carcinoma of the bronchus, in 86, carcinoma of the breast, in 9, mesothelioma and carcinoma of the ovary each, and in 16, other malignancies. There was a total remission of pleural effusions in 42% of the cases, a partial one in 41%, and no effect in 17%. In spite of the relatively large number of patients, some difficulties in interpreting the present results still remain and will be discussed in this paper.