A novel approach to the protection of structural steelwork of composite bridges is proposed by physically changing the environment to which steelwork is exposed. Clean steel does not corrode at relative humidities up to 99% if environmental contaminants are absent. It is apparent that the most critical factor affecting corrosion rates in enclosed spaces is pollution by chlorides and sulphur dioxide and not high relative humidity. A small scale experiment has shown that it is possible simply to enclose the already sheltered steelwork of a composite bridge to produce an environment which is contaminant free and in which corrosion does not take place. It is very reasonable to assume that blast-cleaned painted steel will have a very long maintenance-free life in such environment free from contaminants. There is also interesting preliminary experimental work which indicates that the corrosion rate of pre-corroded speci mens reduces rapidly when introduced into a contaminant-free enclosure. This concept of steelwork enclosure is novel and if the observations and experiments carried out to date are proven correct, potential savings in maintenance painting could be considerable.