Legionnaire's disease and humidifier fever are reviewed in relation to mobile evaporative wetted element type humidifiers. It appears that this equipment is unlikely to be a source of infection but good cleaning routines are advocated. A case study from the Birmingham Museums and Art Gallery, England, illustrates one routine for cleaning/sterilisation/biocide treatment, used mainly on the defensor type humidifiers. The bacteria pseudomonas and achromobacter and the fungi penicillium and trichoderma were identified in the humidifier tanks.