This investigation was designed with the objective of improving on currently available antiemetic regimens to counteract the disabling side effects of cancer chemotherapy. The combination of lorazepam, dexamethasone, and promethazine was compared with dexamethasone and promethazine without lorazepam in a double-blind crossover study. The initial study population consisted of 92 women (most with breast cancer) and 7 men; all received moderately or highly emetogenic chemotherapy. Complete data for both periods of therapy were available for 73 of these patients. Crossover analysis showed a highly significant effect of lorazepam in reducing the severity of nausea (p = .003); the severity of vomiting was also reduced, but less dramatically (p = .051). The frequency of all degrees of nausea and vomiting was less with lorazepam, but the difference was not statistically significant. It is concluded that lorazepam added to dexamethasone and promethazine provides an effective regimen for counteracting the emetic side effects of cancer chemotherapy.