The epidemiological aspects of bacteremias were determined in a university hospital, according to service, age, sex and place of acquisition (nosocomial or community-acquired). From August 1985 through July 1986 the incidence rate of bacteremias at the Sao Paulo Hospital was 21.7/1000 admissions. Such a high rate is probably related to the characteristics of the patients admitted to the hospital. The incidence was higher in the extremes of age and was similar in either sex. Approximately 60% of the bacteremias were nosocomial including 9.1% that were present at admission in patients transferred from other hospitals. The most frequent isolated pathogen was S. aureus. The most important source of bacteremia was the respiratory tract followed by the gastrointestinal and urinary tracts.