Drug treatment for cancer is now widely utilized and in selected neoplasms offers the opportunity for prolonged remission or even cure. Knowledge of the clinical pharmacology of these agents is critically important to successful therapy. Severe and potentially fatal toxicity may occur unless these agents are administered with meticulous attention to details by physicians experienced in their use. Knowledge of functional impairment of organs responsible for the metabolic breakdown or excretion of these agents and awareness of drug-drug interactions are essential in guiding selection and dosage. The late complications that may result are particularly relevant in patients who achieve prolonged remission or cure and in those for whom these agents are used for benign disorders.