Twenty-six clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) collected from six Australian hospitals by a National Staphylococcal Study Group were examined by analysis of restriction fragment length polymorphisms (RFLPs) of chromosomal DNA with pulsed field gel electrophoresis. Digestion with the restriction endonuclease SmaI produced 13-17 bands of 7-700 kb. The digestion patterns were easily distinguished and isolates could be classified into 17 groups based on their RFLPs. Isolates giving a pattern associated with one group were from four hospitals in four different states. In another group, the isolates responsible were from three hospitals in two states and in a further group, the isolates were derived from two hospitals in different states. The remaining groups comprised only one member each. The method has promise for typing and studying the epidemiology of MRSA.