A randomized, double blind crossover trial compared the antiemetic effects of alizapride, a benzamide, and prochlorperazine, a phenothiazine, both administered intravenously to 32 patients treated with chemotherapy combinations containing cisplatin. The total dose of alizapride administered to each patient was 14 mg/kg, and of prochlorperazine .56 mg/kg, divided in five doses. Although alizapride resulted in complete protection against emesis in 31% of the patients during their first course of cisplatin therapy, 42% of those who received alizapride had five or more episodes of emesis. Although prochlorperazine was less effective in offering complete protection against emesis, only 15% of the patients receiving this drug vomited more than five times. The duration of emesis during prochlorperazine treatment was also significantly shorter than during alizapride therapy (p less than 0.02). Optimal dosage and pharmacokinetic distribution of both drugs should be investigated further.