The authors describe their experience with the diagnosis of pulmonary infection with Pneumocystis carinii in patients with malignant diseases. In the course of three years they recorded a total of 16 such cases. All cases were diagnosed by bronchoalveolar lavage. The authors analyze in detail the clinical symptoms and radiological picture. Attention is drawn to the fact that no finding is specific for the disease. The infection of Pneumocystis carinii was combined in 13 cases with another infection. Treatment was successful in 75% of the patients.