Over a 10 month period in a neonatal intensive care unit there was an outbreak of infection caused by Pseudomonas aeruginosa (resistant to ticarcillin, timentin) which involved 24 newborns. There was extensive morbidity and mortality (38%) associated with the infections, which presented as septicaemia (N = 6) (five succumbed and four had coexisting pneumonia), pneumonia (N = 6), meningitis (one, died), conjunctivitis (N = 1), otitis externa (N = 1), conjunctivitis plus otitis externa (N = 1). In addition there were two pseudosepticaemias and six colonized infants, three of whom were treated for the presence of P. aeruginosa in endotracheal aspirates. There was always at least one baby colonized or infected with P. aeruginosa during the outbreak. Environmental surveillance and genomic DNA fingerprinting of isolates identified the blood gas analyzer port as the likely reservoir for the outbreak. Further spread of the organism did not occur after commencement of staff education on vigilant and careful handwashing, especially after use of the blood-gas analyser.