The association of hypercoagulation and cancer, a well established pattern of disease, often leads to pulmonary emboli in an already compromised patient. Anticoagulation therapy in these patients is occasionally complicated by several factors including thrombocytopenia, which may result in a life-threatening situation of hemorrhage versus pulmonary emboli. Mechanical intervention may prevent pulmonary emboli from reaching the lungs, thereby negating the use of anticoagulants in the patient with thrombocytopenia. In this clinical trial, ten patients with cancer and thrombocytopenia complicated by recurrent pulmonary emboli received the Kim-Ray Greenfield filter. There were four men (two with colon carcinoma and two with chronic lymphocytic leukemia) and six women (four with breast carcinoma, one with colon carcinoma, and one with chronic lymphocytic leukemia). Pulmonary emboli were documented in all patients by comparative ventilation/perfusion lung scans, arterial blood gas determinations, and chest x-ray films. In each case anticoagulation was begun, but in six of the ten patients hemorrhage developed and anticoagulation had to be discontinued. The Kim-Ray Greenfield filter was subsequently placed in all ten patients in the infrarenal inferior vena cava (eight via a jugular approach and two via the femoral vein) without complication, and anticoagulation was discontinued. All patients had follow-up to time of death, ranging from six to 26 months (mean 11 months). In no patient was recurrent pulmonary emboli detectable based on clinical evidence, nor in autopsy reports in three of the ten patients. There should be increased usage of the Kim-Ray Greenfield filter in patients with malignancy, thrombocytopenia, and pulmonary emboli.