The RTS,S/AS02A vaccine was safe at all dose levels, in both age groups. No serious adverse events related to vaccination were reported. The frequency of local Grade 3 symptoms was low but tended to increase with increasing dose level. Grade 3 general adverse events in the RTS,S/AS02A groups were infrequent and of short duration. The majority of local and general Grade 3 symptoms resolved or decreased in intensity within 48 h. The pattern and intensity of reactogenicity seen in these studies are similar to those of previous studies with RTS,S/AS02A. All doses were highly immunogenic for anti-CSP and anti-HBsAg antibodies. The pooled anti-CSP antibody data from the two studies showed that the 25 μg dose and 50 μg dose anti-CSP antibody response were similar at both dose levels. However, the immunogenicity of the 10 μg dose anti-CSP response was significantly lower than that of either the 50 μg or 25 μg dose. The 25 μg dose was selected for future studies of RTS,S/AS02A in paediatric populations.