This study compares efficacy, safety and tolerability of 2 and 5 mg tropisetron in prevention of nausea and vomiting induced by low-dose cisplatin- or non-cisplatin-containing chemotherapy. 152 chemotherapy-naïve cancer patients were randomized in a double-blind manner to receive 2 or 5 mg tropisetron intravenously day 1 and orally days 2-6. Primary efficacy criteria were control of acute (day 1) and delayed (days 2-6) vomiting and nausea. Secondary efficacy criteria included overall control (days 1-6) and control of vomiting and nausea by chemotherapy regimen. Safety and tolerability were evaluated clinically, biochemically and by the patient's diary. Only the first cycle was evaluated. 124 of the 144 intention-to-treat patients were evaluable. There was a better total control (no events) of acute vomiting in the 5 mg (73%) than in the 2 mg group (55%, P = 0.02). Total control (< or = 15 minutes) of acute nausea was obtained in 70% of the 5 mg group and in 51% of the 2 mg (P = 0.03). No differences were observed for total control of delayed nausea or vomiting and for the overall outcome of nausea. Less vomiting (days 1-6) occurred in the 5 mg than in the 2 mg group. Efficacy rates ranged widely between chemotherapy regimens, independent of the tropisetron dose groups. There occurred more headache in the 5-mg group (P < 0.05). Once daily 5 mg tropisetron is superior to 2 mg for prevention of acute vomiting and nausea induced by low-dose cisplatin- or non-cisplatin chemotherapy regimens, but causes more headache.