Patients admitted to the Intensive Care Unit (ICU) have a 5-10-fold higher risk for developing nosocomial infection (NI) than in other hospital wards. The constant evolution of epidemiological characteristics of NI in these departments, as well as the growing susceptibility of patients make it necessary to carry out a continuous epidemiological surveillance of these conditions. The aim of this work was, therefore, to know the incidence of nosocomial infection in ICUs, their epidemiological characteristics and the use of antimicrobial agents in infected patients obtained through the information provided by the active surveillance system carried out at Hospital Clínico Universitario, Salamanca, for the 1993-1994 period. The incidence of infected patients and infections were 21.7% and 47.6%, respectively; the mean age of infected patients was 61 +/- 9.6 years and 29.6% of patients died. Sixty-four percent of infections corresponded to pneumonia and bacteremia, with incidences of 15.5% and 14.9%, respectively. The main responsible agents for pneumonia, bacteremia, surgical wound infection, urinary tract infection were P. aeruginosa, S. epidermidis, Enterococcus sp., and Candida sp., respectively. All infected patients had a central catheter in place an 57.7% were under mechanical ventilation. The most commonly used antimicrobial agents were amikacin, ceftazidime, cefotaxime, vancomycin, metronidazole, and gentamicin.