Clinical and laboratory features were analyzed in 277 patients with 279 episodes of E. coli bacteremia, treated at the University Hospital of Infectious Diseases "Dr Fran Mihaljević"c, Zagreb between 1980 and 1989. Patients ranged in age from 4 days to 91 years. Thirty-two per cent of patients were male and 68% were female. The majority of patients had underlying disease which was considered not to be fatal within the next five years (57%) or they were completely healthy (34%). Four per cent of bacteremias were polymicrobic and 13% were considered nosocomial in origin. The clinical source of bacteremia was known in 84%. In community-acquired bacteremia, the urinary tract was the most frequent site of origin (78%) and in nosocomial-acquired bacteremia the source could not be identified (54%). Septic shock occurred in 24% of the patients and coagulation abnormalities were observed in 41% of the patients. Fatal outcome was registered in 10% of the patients. Mortality was higher among males (16%:7%) up to 2 months of age (29%) and above 60 years (15%), and in those with nosocomial-acquired bacteremia (49%), polymicrobial (50%) and recurrent bacteremia (50%), as well as in patients with severe underlying disease (29-75%). Mortality was lower in patients who were given an early appropriate antimicrobial therapy. The advantage of combinations of antimicrobial therapies over monotherapy could not be demonstrated among patients in each category of severity of underlying host disease.