One hundred and eight patients selected to receive combinations of highly emetic cytotoxic chemotherapy for malignant disease were included in a study of anti-emetic therapy. The patients were randomly allocated to receive levonantradol (0.5, 0.75 or 1 mg) or chlorpromazine (25 mg) prior to receiving their first course of cytotoxic therapy. The appropriate anti-emetic was administered 2 hr prior to the start of chemotherapy, 2 hr after chemotherapy and subsequently at 4-hourly intervals for a further 8 hr. The extent of anorexia, nausea and vomiting along with other side-effects were assessed at regular intervals by physicians and nursing staff during the 24 hr following chemotherapy. In addition, a self-assessment questionnaire was completed by the patients. Levonantradol (0.5 mg) was superior to chlorpromazine (25 mg) as an anti-emetic. Both were reasonably well tolerated, although at this dose of levonantradol 22% of patients experienced dysphoric reactions. At higher doses of levonantradol the proportion of patients experiencing these reactions rose to 50%, but without a concomitant increase in antiemetic activity. Neither drug achieved satisfactory control of vomiting in patients receiving combinations containing cis-platinum. We conclude that levonantradol (0.5 mg) is a more effective anti-emetic than chlorpromazine (25 mg) in patients receiving cytotoxic chemotherapy. However, its use cannot be recommended due to its high incidence of unacceptable central nervous system side-effects.