Irinotecan (CPT-11) is a derivative of the chemotherapeutic agent camptothecin. CPT-11 inhibits the nuclear enzyme topoisomerase I. It has demonstrated a broad spectrum of antitumor activity in preclinical tumor model systems. Significant advances have been made toward the understanding of the pharmacokinetics and schedule dependency of this agent. CPT-11 has demonstrated significant clinical activity in the treatment of patients with gastrointestinal, pulmonary, gynecologic, and lymphoid malignancies. Further study of this agent to determine its role in combination chemotherapeutic regimens is currently underway.