Because there is little information about the frequency of carriage of various species of coagulase-negative staphylococci (CNS) in hospital staff, we prospectively investigated nasal CNS in patients and personnel in a Surgical Intensive Care Unit (SICU). The majority of CNS from personnel were Staphylococcus epidermiditis. The CNS species from patients on admission were more diverse and included multiply antibiotic-resistant S. haemolyticus. Patients' CNS became more like CNS colonizing personnel after admission with respect to both antimicrobial susceptibility and speciation. Plasmid and antibiotic sensitivity profiles of S. epidermidis resistant to multiple antibiotics from five patients were identified as those from one employee, but there was no evidence that this was of clinical significance. A variety of factors influence nasal colonization by CNS in SICUs. The nasal CNS of patients change after admission and may become more resistant and less diverse. The factors influencing changes in the antibiotic susceptibility and the aetiology of CNS infection require further study.