A method and a device for replacing objective parts, especially of a projection or illumination objective for microlithography in which an objective having an objective interior and objective parts provided therein is provided. At least one objective part is replaceably accommodated in the objective. Immediately prior to installation in the objective, the replaceable objective part is cleaned outside the objective interior in at least one cleaning room sealed off from the ambient atmosphere. Immediately after cleaning, the replaceable objective is installed in the objective without contact with the normal ambient atmosphere.