 This randomized, controlled, double-blinded, dose-ranging, Phase I-II study in 600 healthy adults, 18 to 49 years old, is designed to investigate the safety, reactogenicity, and dose-related immunogenicity of an investigational inactivated influenza AH5N1 virus vaccine when given alone or combined with aluminum hydroxide. A secondary goal is to guide selection of vaccine dosage levels for expanded Phase II trials based on reactogenicity and immunogenicity profiles. This dose optimization will be applied to both younger and older subject populations in subsequent studies. Subjects who meet the entry criteria for the study will be enrolled at one of 4 study sites and will be randomized into one of 8 groups to receive 2 doses of influenza AH5N1 vaccine containing 3.75, 7.5, 15, or 45 mcg of HA with or without aluminum hydroxide adjuvant by intramuscular injection. Participants may be involved in study related procedures for up to 8 months. 