Diarrhea is a well-recognized side effect of chemotherapy, which affects the quality of life and when refractory is potentially life threatening. Irinotecan (CPT-11) is associated with an elevated incidence of chemotherapy-induced diarrhea and subsequent morbidity. Standard antidiarrheal treatment is based on high-dose loperamide, but this agent is associated with a significant failure rate. Octreotide is active against chemotherapy-induced diarrhea caused by fluoropyrimidines and irinotecan, with a distinct mechanism of action. We administered octreotide in a phase I trial in 37 patients who received irinotecan and experienced loperamide-refractory diarrhea, 23 of whom experienced grade III-IV diarrhea and were treated with loperamide. The 13 patients in whom to loperamide failed to control diarrhea received octreotide, with a high response rate (92%). We conclude that octreotide is effective against loperamide-refractory diarrhea resulting from irinotecan-based chemotherapy.