We conducted a randomized, double-blind, crossover study comparing the antiemetic efficacy of dexamethasone and prochlorperazine in 42 patients with cancer who were receiving outpatient chemotherapy, mainly without cisplatin. Patients experienced significantly less nausea and vomiting with dexamethasone than with prochlorperazine (P less than 0.02 and less than 0.03, respectively). Twenty-five patients experienced no nausea with dexamethasone, as compared with 14 patients taking prochlorperazine (P less than 0.001). Similarly, 29 patients receiving dexamethasone did not vomit, as compared with 18 receiving prochlorperazine (P less than 0.001). Somnolence was the most frequent side effect, occurring in 60 per cent of patients receiving prochlorperazine and in 12 per cent of those receiving dexamethasone (P less than 0.001). Patients also experienced less suppression of appetite while receiving dexamethasone (P less than 0.02). We conclude that dexamethasone is an effective and safe antiemetic in patients receiving cancer chemotherapy without cisplatin.