Suramin is a new experimental polyanionic compound that has shown evidence of antitumor activity in patients with hormone refractory prostate cancer. After a few years of Phase I and Phase II testing, much of the drug's toxicity pattern has been carefully characterized. Similarly, pharmacologic studies have defined many of the drug's complex pharmacologic properties to the extent that simple outpatient methods of drug administration can be easily accomplished. A pharmacologically derived, fixed outpatient schedule has been shown to be safe and effective and is currently in active Phase III development in prostate cancer and will provide more definitive data regarding the role of suramin in the treatment of this disease. Despite these accomplishments, a number of questions require further study, such as definition of pharmacodynamic correlations, effects on the hypothalamic‐pituitary‐adrenal and gonadal axis, and the nature of its most common dose‐limiting toxicity, which is a syndrome of malaise and fatigue. Cancer 1995;75:1927–34.