Recently an immunoblotting system was developed for typing oxacillin-resistant Staphylococcus aureus. Oxacillin-resistant S. aureus (ORSA) isolates recovered during a 4-month period from premature new-borns division of University Hospital of Pavia, with several antimicrobial susceptibility patterns, were evaluated with this typing scheme. Immunoblotting was found to be a useful method with good reproducibility and the ORSA strains isolated at our institution were differentiated in two major groups of organisms clinically and epidemiologically related. Furthermore immunoblot typing showed same specific correlations with susceptibility patterns of ORSA isolates studied.