We have investigated the pharmacokinetics of a 5-day multiple oral dose of 5 mg tropisetron capsule in patients with malignant tumour who had received cisplatin single administration. Its anti-emetic effects on acute and delayed emesis and vomiting were also investigated. During the 5 days after this administration, changes in the release and metabolism of serotonin were investigated. The results may be summarized as follows: 1) The pharmacokinetic parameters of tropisetron revealed no significant change in the data between day 1 and day 5. Also, the parameters were almost similar to those observed in healthy adult males (clinical phase I study); Cmax. T1/2 and AUC 0-24 hrs on day 1 were 9.1 +/- 2.1 ng/ml, 12.5 +/- 4.2 hrs, 85.5 +/- 22.7 ng.hr/ml, respectively. The urinary excretion of the parent drug up until 24 hours after administration on day 1 was 3.8% of the dose administered and 2.9% of the total dose after the last administration; no difference in the urinary excretion rate was observed in healthy subjects. It was thus suggested that hydration accompanied by cisplatin administration did not affect the pharmacokinetics of tropisetron. 2) The changes in the amount of urinary excretion of 5-hydroxy-indoleacetic acid (5-HIAA) during 5 days after cisplatin administration were observed; urinary excretion of 5-HIAA increased 2.3 times (1.3-5.4 times) the baseline on the average during 6 to 12 hours on day 1. In 6 out of 10 patients, the increases in urinary excretion of 5-HIAA showed double or more the baseline during 2 to 5 days after cisplatin administration. Serotonin was thus deemed to be related to the development of delayed emesis. 3) The anti-emetic effects of tropisetron on acute and delayed emesis and vomiting were rated as "markedly effective" in 6 out of 11 patients (54.6%) and "effective" in 1 out of 11 patients (9.1%) on day 1; vomiting did not occur in any of these 7 patients. Tropisetron also controlled emesis and vomiting during days 2-5, and was rated as "almost favorable" in 6 out of 11 patients (54.5%). Further, in 4 out of 6 patients, in whom the urinary excretion of 5-HIAA was increased on day 2 onwards, vomiting did not occur during the time when the urinary excretion of 5-HIAA was increasing. On the basis of the above results, tropisetron is deemed to have certain antiemetic effects on delayed vomiting as well. Its 5-HT3 receptor mediated mechanism was similarly seen to inhibit acute nausea and vomiting.