OUTLINE: This is a randomized, double blind, placebo controlled, multicenter study. Patients are stratified according to abdominal carcinomatosis (yes vs no), renal insufficiency (creatinine less than 2.0 mg/dL vs creatinine at least 2.0 mg/dL), type of cancer (brain vs gastrointestinal vs other), and narcotic use (yes vs no). Patients are randomized to one of two treatment arms. Arm I: Patients receive oral ondansetron twice daily on days 1-7 and oral placebo twice daily on days 8-14 in the absence of unacceptable toxicity. Arm II: Patients receive oral placebo twice daily on days 1-7 and oral ondansetron twice daily on days 8-14 in the absence of unacceptable toxicity.