In order to inhibit the nausea and vomiting induced by oral anticancer drugs, granisetron was administered orally at a dose of 2 mg once a day, and its usefulness and safety were evaluated. The subjects were 26 outpatients with gastric or colon cancer receiving chemotherapy with oral anticancer drugs and complaining of gastrointestinal symptoms. A record sheet was handed to the patients. In comparison with the condition before treatment, the patients were instructed to indicate on the record sheet the severity of nausea (4 grades), presence or absence of vomiting, and degree of appetite (4 grades) after treatment, and thereby to evaluate the clinical efficacy or antiemetic effect every day in accordance with clinical efficacy evaluation criteria of 4 grades (very effective, effective, slightly effective, and ineffective). i) Nausea disappeared in 47.8% of the patients on the 1st day of treatment and in 65.2% on the 5th day of treatment. ii) Vomiting was observed in 2 and 3 patients on the 1st and 3rd day, respectively, but not on the 4th day of treatment or thereafter. iii) The efficacy rate, comprising both very effective and effective, was 69.5% on the 1st day of treatment, and increased gradually to reach 78.2% on the 5th day of treatment. iv) There was no adverse reaction or abnormality of laboratory test values attributable to granisetron. Granisetron was safe and effective against nausea and vomiting induced by oral anticancer drugs.