Surveillance data on 12,944 bacterial isolates derived from nosocomial infections, reported to the Department of Microbiology and Infectious Diseases of the Hellenic Air Force and VA General Hospital over a 9-year period (1986-1994), were analyzed by the use of a microbial infection control software system. Overall, the isolation rate of Escherichia coli decreased from 25.2% in 1986 to 18.2% in 1994 and Proteus spp. from 5.3 to 2.6%. Remarkably, Pseudomonas spp. increased from 7.2 to 11.3%, Enterobacter spp. from 1.6 to 5.1%, Klebsiella spp. from 5.9 to 7.8% and Enterococcus spp. from 3 to 7.4%. Interestingly, the above phenomenon was paralleled by a significant increase in resistance rate to various antibiotics. Specifically, Staphylococcus aureus and coagulase-negative staphylococci, though they did not display any significant variation in isolation rates, showed an alarming increase in resistance rate to oxacillin, from 11 and 21% in 1986 to 51 and 75% in 1994, respectively. Enterococcus spp. sensitivity to vancomycin remained unlatered at 90%. The above-mentioned serious shift towards more resistant bacteria should be a matter of consideration.