Hepatic arterial infusion (HAI) of floxuridine is often used for metastatic colorectal cancer, though this is associated with dose-limiting hepatobiliary toxicity. A phase I trial was initiated to determine if circadian-patterned HAI floxuridine would reduce toxicity. Twenty-one patients were enrolled, and they received a continuous 14-day HAI of floxuridine, with 90-95% of the drug delivered over the same six-hour period daily. The therapy was tolerable, but there was no reduction in hepatobiliary toxicity. The response rate of 33% (1 complete and 6 partial responses) was similar to that of regimens that do not utilize circadian timing. HAI floxuridine chronotherapy for metastatic colorectal cancer cannot be recommended.