The immunogenicity and safety profile of an inactivated whole-virion influenza A (H5N1, NIBRG-14) vaccine with alum adjuvant that was administered by IM or SC injection in a phase I clinical study involving 120 healthy Japanese men aged 20-40 years is described. The serological response of the IM group was stronger than that of the SC group. Local adverse events were less severe with IM injection than with SC injection, while similar systemic adverse events were seen in both groups. These results indicate that, when administering an inactivated whole virion vaccine with alum adjuvant for pandemic influenza, IM injection may achieve better immunogenicity and safety than SC injection.