The purpose of this study was to compare the objective response rate, duration of remission, and survival of 5-fluorouracil (5-FU) versus those of 5-FU plus levamisole in metastatic colorectal cancer using the same dose and schedule of these agents as in the North Central Cancer Treatment Group and intergroup studies of adjuvant therapy. Patients with no prior history of chemotherapy for metastatic disease were entered on this Hoosier Oncology Group randomized Phase III trial. Patients were stratified by Karnofsky performance status and presence or absence of liver metastases. They were randomized to receive 450 mg/m2 5-FU i.v. for 5 days followed by 15 mg/kg i.v. weekly (arm 1) or the same dose of 5-FU plus levamisole 50 mg p.o. every 8 h for 3 days every 2 weeks (arm 2). The duration of treatment for both arms was 26 weeks. From April 1990 to March 1995, 199 patients were entered. One hundred eighty-two patients, 91 in each arm, were fully evaluable. The response rates were 12% on arm 1 and 13% on arm 2. The median duration of response was 18 weeks on both arms. The median survival was 48 weeks on arm 1 and 41 weeks on arm 2 (P = 0.20). This study failed to show any improvement in survival, response, or duration of remission with the addition of levamisole to 5-FU in the treatment of metastatic colorectal cancer.