Lorazepam was compared to placebo to assess its control of nausea and vomiting in patients receiving cytotoxic chemotherapy and prochlorperazine. The study design was a randomized, double-blind crossover in which three consecutive chemotherapy courses were compared so that each patient acted as his or her own control. Of 107 patients entered, 80 were evaluable for analysis. Lorazepam significantly reduced the severity and duration of nausea, the severity of vomiting, and the number of vomiting episodes when compared to placebo. Anxiety was reduced during lorazepam courses but not significantly when compared to placebo. There was significantly more sedation with lorazepam courses. Overall, patients preferred lorazepam courses although this preference was significant only in the patient subset receiving doxorubicin and cyclophosphamide. Lorazepam is a useful adjunct to prochlorperazine in patients receiving cytotoxic chemotherapy.