Suramin sodium is an aromatic polysulfonated compound that was originally introduced as an antiparasitic agent in the 1920s. Recently, in view of its ability to bind and disrupt the function of multiple growth factors and cellular enzyme systems, the authors have been evaluating the role of suramin as an antitumor agent. In this study, 12 patients with metastatic renal cell carcinoma received parenteral suramin by continuous infusion to a peak plasma suramin level greater than 200 micrograms/ml. No objective radiographic responses were observed, although greater than 90% necrosis of multiple tumor sites was documented at autopsy in one patient and normalization of tumor-related hypercalcemia occurred in another patient. Two patients had stable disease of 10 and 28 weeks' duration, respectively. Significant toxicities included hypotension related to sepsis and resulting in renal insufficiency (one patient), development of liver function abnormalities (one patient) marked thrombocytopenia (one patient), prothrombin time prolongation (all patients), vortex keratopathy (two patients), and Grade 1 sensory neuropathy (two patients). On the basis of the current results, suramin does not appear to be an active single agent against metastatic renal cell carcinoma when administered by this dosing schedule.