The results of hospital infection surveillance over an eight-month period in the Intensive Care Unit (ICU) of the University Hospital of Infectious Diseases "Dr Fran Mihaljević", Zagreb, are presented together with the results of the antibiotic resistance of isolated gram-negative bacteria in relation to the clinical material taken for culture. Of 110 strains of gram-negative bacteria isolated, 103 (93.6%) were resistant to ampicillin, 80 (72%) to gentamicin, 74 (67%) to cefotaxime, 50 (45.5%) to pefloxacin. Imipenem, ciprofloxacin, ceftazidime and amikacin were the most active representatives of their respective groups with 5, 25, 49 and 50% of resistant strains. Strains isolated in urinary tract infections were significantly less resistant to amikacin and ceftazidime (p < 0.05) than strains isolated from other sources. Our findings stress the need for close surveillance of antibiotic resistance in these selected groups of patients, and are particularly relevant for planning empirical anmtibiotic therapy of hospital infection in the ICU.