The purpose of this study was the evaluation of the effectiveness of intrapericardial administration of tetracycline, 5-fluorouracil and cisplatin in patients with recurrent malignant pericardial effusion. In 33 cases with malignant pericardial effusion 46 pericardiocenteses under two-dimensional echo-cardiography were performed. No complications were observed after this procedure. Pericardiocentesis was followed by catheterization of the pericardial space for a mean period of 15 days (range 1-64). In 4 cases bacterial pericarditis was observed during catheterization. The mean volume of the pericardial fluid was 2.41 (range 0.4-13 l). In cases with bloody pericardial fluid the PO2, PCO2 and pH of the fluid were estimated and the results compared with the values for venous blood obtained from the upper limbs. Highly statistically significant differences were documented. Twenty cases of malignant pericardial effusion were treated with direct pericardial administration of cisplatin, 3 with 5-fluorouracil and 2 with tetracycline. Good results (no fluid reaccumulation) were observed only after cisplatin therapy. We conclude that pericardiocentesis performed under two-dimensional echo cardiography, followed by pericardial catheterization and direct pericardial treatment with cisplatin are the methods of choice in cases with malignant pericardial effusion. In cases with bloody pericardial fluid PO2, PCO2 and pH analysis can be useful to differentiate the source of the bloody fluid (blood or bloody fluid).