A controlled double-blind study of five orally administered antiemetic agents and a placebo was carried out during the administration to patients of a known emetic agent, fluorouracil. One hundred eighty patients were observed during their first course of treatment with fluorouracil and 120 patients during their second course. Thiopropazate and prochlorperazine showed a statistically significant therapeutic advantage over the placebo. Pipamazine, cinnarizine, and trimethobenzamide were progressively less effective, although each appeared to exert some antiemetic effect. Those agents showing the greatest antiemetic potency also showed the highest incidence of oversedation.