A method of simultaneously applying three different diffusion aluminide coatings to a metal part with an external surface and internal passageways includes first placing the part in an enclosed retort. Areas of the part are then coated with aluminum containing slurry for a first diffusion aluminide coating. Interior walls of the retort are then coated with a vapor source slurry for a second vapor phase aluminide coating on the surface of the part. Areas on the surface of the part not requiring coating are coated with masking materials. A closed chamber inside the retort containing source material for a third vapor phase diffusion aluminide coating for the internal passageways is then attached to the internal passageways. The retort is then placed in a furnace under a protective atmosphere and subjected to a diffusion heat treat to coat the external surfaces and internal passageways with the three different aluminide coatings.