Objectives: In recent years, a sharp increase has been noted in The E. Wolfson Hospital, Holon, Israel, in the isolation rate of enterococci from urine samples. The purpose of the study was to examine whether this phenomenon was associated with a change in antibiotic use in the institution. Methods: The isolation rate of enterococci from urine samples and the amount of fluoroquinolones and cephalosporins utilized in three periods during 1987, 1990, and 1993 were calculated. Results: Fluoroquinolones were introduced in The E. Wolfson Hospital in 1988. Between 1990 and 1993, both the use of fluoroquinolones and the isolation of enterococci increased by 50%. No change in the use of cephalosporins was observed during the same period. Conclusions: The effect of the extensive use of fluoroquinolones on colonization by, and superinfection with enterococci is explained by the broad antibacterial spectrum of these agents on one hand and their mediocre in vitro activity against enterococci on the other. This association is particularly worrisome since it may contribute indirectly to the spread of vancomycin-resistant enterococci.