There is a high incidence of primary renal tubule damage among patients with malignant disease who die following recent treatment with combinations of cephalothin and gentamicin. Administration of this combination of antibiotics appears to make the patient appreciably more susceptible to severe renal injury if an additional, often minor, insult to the renal tubules is superimposed. In the present study, significant blood loss or bacterial infection not promptly controlled by the antibiotic combination were two factors that provided this additional insult to many patients; the renal injury in these patients could not be attributed to bleeding or infection alone. The combination of cephalothin plus gentamicin carries the potential of causing renal tubule injury and places the patient severely ill with malignant disease at risk for renal failure from many clinical complications which are commonly associated with their primary illness.