AS04 (Aka. "Adjuvant System 04") is a trade name for combination of adjuvants used in various vaccine product by GlaxoSmithKline (GSK), in particular the Fendrix Hepatitis B vaccine. It consists of aluminum hydroxide and monophosphoryl lipid A (MPL). Furthermore it is the successor of AS03 which is a Squalene based adjuvant approved for pandemic vaccine by the EMA.