A total of 24 patients who were receiving combination chemotherapy (POMB) including cisplatin at a dose of 100-120 mg/m2 were treated with the 5HT3 antagonist GR38032F (GR) as an anti-emetic prophylaxis. GR was given as a 15-min loading infusion followed by a 24-h infusion at three escalating dose levels of 1, 2 and 4 mg/h. In the first 24 h after commencing treatment, six patients had complete control of nausea and vomiting (CR), two had 1-2 emetic episodes (MR) and five had 3-5 emetic episodes (mR). The major response rate (CR + MR) was thus 35%. Eight responding patients (CR or MR) went on to receive oral GR at 8 or 12 mg t.i.d. for 5 days. In this group there was one CR, one MR, two mRs and four failures (F). There was no evidence of an improved therapeutic effect with increasing dose in either the infusion or the oral section of the study, although numbers were limited in the latter part of the trial. Toxicity was mild, with low-grade headache affecting 25% of patients being the most frequent side effect. Pharmacokinetic data was obtained in six patients at each dose level. There was a progressive rise in clearance with increasing dose, indicating that the kinetics are non-linear. However, there was no evidence of an association between high plasma levels and therapeutic efficacy. GR38032F is well tolerated and has promising single-agent activity in preventing vomiting induced by high-dose cisplatin.