Between 1986 and 1989 a single strain of a methicillin- and multiply-resistant Staphylococcus aureus caused three distinct outbreaks at Utrecht University Hospital, involving 11, 19 and 32 patients, respectively. In all three episodes, members of staff were screened for MRSA carriage, and 58 persons were found to have positive nose cultures. In each outbreak it became necessary to isolate colonized and infected patients on a separate isolation ward. Staff carriers were also treated. Over the 18 months since the last outbreak, no new acquisitions of this epidemic MRSA strain have occurred. Between 1986 and 1989, the strain which caused the three outbreaks was not the only MRSA strain which was introduced into the hospital. Six other strains, which differed from the epidemic strain as shown by phage typing and antimicrobial susceptibility pattern, were found in single patients. The experience at Utrecht University Hospital illustrates the need for strict measures to eradicate epidemic strains of MRSA as well as the differences in "epidemicity" among various strains of MRSA.