We investigated contamination of environmental surfaces by Staphylococcus aureus from April 1 to the end of June in 2002 in the dermatological ward (37 beds) of a university hospital. For surfaces contaminated by high levels of S. aureus, disinfection methods were evaluated. 100-10 5 colony forming units (cfu) of methicillin-resistant S. aureus (MRSA) or methicillin-sensitive S. aureus (MSSA) were detected on items such as an immersion bathtub (examined area, about 900 cm 2 ), foot washbowl, stretcher for an immersion bath, and chair for the shower. After disinfection, no S. aureus was detected on smooth surfaces such as the immersion bathtub and foot washbowl; however, S. aureus was detected even after disinfection on porous surfaces made of sponge-like materials (polyethylene foam) such as the stretcher for the immersion bath and the shower chair. Scanning electron microscopy of the porous surfaces showed formation of a large amount of coccus and bacillus biofilms on the walls of pores in the multi-pore structure. Material that is porous should not be used in patient care settings because it is not possible to disinfect it properly.