Diarrhea is one of dose-limiting factors of irinotecan (CPT-11) and its incidence is over 60% in patients receiving this drug. Therefore, it is important to prevent diarrhea for more effective use of CPT-11. We used Hange-shashinto (TJ-14), an ethical Kampo (Chinese herb) Medicine, to prevent diarrhea induced by CPT-11. Twenty-three patients (9 lung cancer, 4 pancreatic cancer, 2 colorectal cancer, 4 malignant lymphoma, and 4 other types of cancer) entered in this study. All patients were treated with CPT-11 in combination with oral TJ-14 (7.5 g t.i.d.) every day starting prior to CPT-11 infusion. The dose of CPT-11 was 60-100 mg/m2/w, 120-150 mg/m2/2 w or 40 mg/m2/d x 3 days/w. Three of 23 patients could not evaluate the efficacy and safety of TJ-14 since they could not take TJ-14 due to its odor and taste. The efficacy and safety of TJ-14 was not evaluated in one patient also since the patient could not continue taking TJ-14 due to vomiting induced by CPT-11. Nine patients showed an excellent response (no diarrhea or only 1 day of ECOG Grade 1 diarrhea). 9 showed a good response (Grade 1 diarrhea that disappears within 3 days) and one did not reveal response. It is suggested that TJ-14 possesses a preventive effect against diarrhea induced by CPT-11.