The safety and efficacy of the new 5HT-3 antagonist granisetron as an antiemetic in children with cancer was evaluated in 40 children at a single dose of 40 micrograms/kg. No adverse affects attributable to the granisetron were noted. The overall major and complete response rate was 82.5% and this was highest in the younger children. Only 2 patients showed no response. Pharmacokinetic studies showed associations between some pharmacokinetic parameters and age which were no longer apparent after normalisation for body weight. Granisetron is an effective and very well-tolerated antiemetic and appears to be an important addition to the supportive care available for children with cancer.